Polyester Resins for High-Strength Articles

ABSTRACT

The present invention relates to slow-crystallizing, titanium-catalyzed polyethylene terephthalate resins that are useful for making high-strength, high-clarity bottles that possess improved resistance to stress cracking and thermal creep. The polyethylene terephthalate resins possess improved reheating profiles and are especially useful for making polyester articles that have exceptional clarity, dimensional stability, and thermal stability.

CROSS-REFERENCE To COMMONLY ASSIGNED APPLICATIONS

This application is a continuation of commonly assigned U.S. patentapplication Ser. No. 12/622,502 for Polyester Resins for High-StrengthArticles, filed Nov. 20, 2009, (and published Sep. 2, 2010, asPublication No. 2010/0221472 A1).

Parent U.S. patent application Ser. No. 12/622,502 is a continuation ofcommonly assigned U.S. patent application Ser. No. 12/334,851, forPolyester Resins for High-Strength Articles, filed Dec. 15, 2008, (andpublished Jul. 9, 2009, as Publication No. 2009/0176046 A1), whichitself is a continuation of commonly assigned U.S. patent applicationSer. No. 11/466,066, for Polyester Resins for High-Strength Articles,filed Aug. 21, 2006, (and published Mar. 15, 2007, as Publication No.2007/0059465 A1), which itself is a continuation-in-part of commonlyassigned U.S. patent application Ser. No. 10/996,789, for PolyesterPreforms Useful for Enhanced Heat-Set Bottles, filed Nov. 24, 2004, (andpublished Jul. 14, 2005, as Publication No. 2005/0153086 A1), now U.S.Pat. No. 7,094,863, which itself is a continuation-in-part of commonlyassigned U.S. patent application Ser. No. 10/850,918, forSlow-Crystallizing Polyester Resins, filed May 21, 2004, (and publishedNov. 25, 2004, as Publication No. 2004/0236066 A1), now U.S. Pat. No.7,129,317.

Parent U.S. patent application Ser. No. 11/466,066 is also acontinuation-in-part of commonly assigned International PatentApplication No. PCT/US04/39726 for Methods of Making Titanium-CatalyzedPolyethylene Terephthalate Resins, filed Nov. 24, 2004, (and publishedNov. 3, 2005, as Publication No. WO 2005/103110), which itself is acontinuation-in-part of U.S. patent application Ser. No. 10/850,269, forMethods of Making Titanium-Catalyzed Polyester Resins, filed May 20,2004, (and published Nov. 24, 2005, as Publication No. 2005/0261462 A1)and the aforementioned U.S. patent application Ser. No. 10/850,918, nowU.S. Pat. No. 7,129,317.

Each of these foregoing patents, patent application publications, andpatent applications is hereby incorporated by reference in its entirety.

This application, via parent U.S. patent application Ser. No.11/466,066, further claims the benefit of the followingcommonly-assigned, provisional patent applications: U.S. ProvisionalPatent Application Ser. No. 60/738,867, for Melt-Phase Polycondensationof Titanium-Catalyzed PET Resins, filed Nov. 22, 2005; U.S. ProvisionalPatent Application Ser. No. 60/739,796, for Polyester Resins forHigh-Strength Articles, filed Nov. 23, 2005; U.S. Provisional PatentApplication Ser. No. 60/739,498, for Polyester Resins forHigh-Efficiency Injection Molding, filed Nov. 23, 2005; and U.S.Provisional Patent Application Ser. No. 60/739,645, for PolyalkyleneTerephthalate Resins for High-Strength Articles, filed Nov. 23, 2005.

Each of these foregoing provisional applications is hereby incorporatedby reference in its entirety.

This application further incorporates entirely by reference thefollowing related patent applications, each of which is commonlyassigned: U.S. Provisional Patent Application Ser. No. 60/472,309, forTitanium-Catalyzed Polyester Resins, Preforms, and Bottles, filed May21, 2003; U.S. Provisional Patent Application Ser. No. 60/559,983, forTitanium-Catalyzed Polyester Resins, Preforms, and Bottles, filed Apr.6, 2004; U.S. Provisional Patent Application Ser. No. 60/573,024, forSlow-Crystallizing Polyester Resins and Polyester Preforms HavingImproved Reheating Profile, filed May 20, 2004; and International PatentApplication No. PCT/US04/16375 for Slow-Crystallizing Polyester Resins,filed May 21, 2004, (and published Dec. 2, 2004, as Publication No. WO2004/104080).

The foregoing non-provisional and international applications claimpriority, either directly or indirectly, to the aforementionedprovisional applications, namely U.S. Provisional Patent ApplicationSer. No. 60/472,309, U.S. Provisional Patent Application Ser. No.60/559,983, and/or U.S. Provisional Patent Application Ser. No.60/573,024.

This application incorporates entirely by reference the followingcommonly assigned patent and patent applications, which disclose polymerresins and polymer processes: U.S. patent application Ser. No.09/456,253, filed Dec. 7, 1999, for a Method of Preparing ModifiedPolyester Bottle Resins, now U.S. Pat. No. 6,284,866; U.S. patentapplication Ser. No. 09/851,240, filed May 8, 2001, for a Method ofPreparing Modified Polyester Bottle Resins, now U.S. Pat. No. 6,335,422;U.S. patent application Ser. No. 11/046,481, for Methods of MakingImide-Modified Polyester Resins, filed Jan. 28, 2005, (and publishedAug. 4, 2005, as Publication No. 2005/0171326 A1); International PatentApplication No. PCT/US05/03149 for Imide-Modified Polyester Resins andMethods of Making the Same, filed Jan. 28, 2005, (and published Aug. 11,2005, as Publication No. WO 2005/073272); and International PatentApplication No. PCT/US06/02385 for Improved Polyamide-Polyester PolymerBlends and Methods of Making the Same, filed Jan. 23, 2006, (andpublished Jul. 27, 2006), as Publication No. WO 2006/079044.

This application further incorporates entirely by reference thefollowing commonly assigned patents and patent applications, whichdisclose methods for introducing additives to polymers: Ser. No.08/650,291 for a Method of Post-Polymerization Stabilization of HighActivity Catalysts in Continuous Polyethylene Terephthalate Production,filed May 20, 1996, now U.S. Pat. No. 5,898,058; Ser. No. 09/738,150,for Methods of Post-Polymerization Injection in Continuous PolyethyleneTerephthalate Production, filed Dec. 15, 2000, now U.S. Pat. No.6,599,596; Ser. No. 09/932,150, for Methods of Post-PolymerizationExtruder Injection in Polyethylene Terephthalate Production, filed Aug.17, 2001, now U.S. Pat. No. 6,569,991; Ser. No. 10/017,612, for Methodsof Post-Polymerization Injection in Condensation Polymer Production,filed Dec. 14, 2001, now U.S. Pat. No. 6,573,359; Ser. No. 10/017,400,for Methods of Post-Polymerization Extruder Injection in CondensationPolymer Production, filed Dec. 14, 2001, now U.S. Pat. No. 6,590,069;Ser. No. 10/628,077, for Methods for the Late Introduction of Additivesinto Polyethylene Terephthalate, filed Jul. 25, 2003, now U.S. Pat. No.6,803,082; and Ser. No. 10/962,167, for Methods for IntroducingAdditives into Polyethylene Terephthalate, filed Oct. 8, 2004, (andpublished Aug. 4, 2005, as Publication No. 2005/0170175 A1).

This application further incorporates entirely by reference thefollowing commonly assigned patents and patent applications, whichdisclose polymer resins having reduced frictional properties andassociated methods: Ser. No. 09/738,619, for Polyester Bottle ResinsHaving Reduced Frictional Properties and Methods for Making the Same,filed Dec. 15, 2000, now U.S. Pat. No. 6,500,890; Ser. No. 10/177,932for Methods for Making Polyester Bottle Resins Having Reduced FrictionalProperties, filed Jun. 21, 2002, now U.S. Pat. No. 6,710,158; and Ser.No. 10/176,737 for Polymer Resins Having Reduced Frictional Properties,filed Jun. 21, 2002, now U.S. Pat. No. 6,727,306.

BACKGROUND OF THE INVENTION

Because of their strength, heat resistance, and chemical resistance,polyester containers, films, sheets, and fibers are an integralcomponent in numerous consumer products manufactured worldwide. In thisregard, most commercial polyester used for polyester containers, films,and fibers is polyethylene terephthalate polyester.

Polyester resins, especially polyethylene terephthalate and itscopolyesters, are also widely used to produce rigid packaging, such astwo-liter soft drink containers. Polyester packages produced bystretch-blow molding possess outstanding strength and shatterresistance, and have excellent gas barrier and organoleptic propertiesas well. Consequently, such lightweight plastics have virtually replacedglass in packaging numerous consumer products (e.g., carbonated softdrinks, fruit juices, and peanut butter).

In conventional processes for making polyester resins, modifiedpolyethylene terephthalate resin is polymerized in the melt phase to anintrinsic viscosity of about 0.6 deciliters per gram (dL/g), whereuponit is further polymerized in the solid phase to achieve an intrinsicviscosity that better promotes bottle formation. Thereafter, thepolyethylene terephthalate may be formed into articles, such as byinjection molding preforms, which in turn may be stretch-blow moldedinto bottles.

Unfortunately, at normal production rates, most polyester resins cannotbe efficiently formed into preforms and bottles that are suitable forhot-fill applications. Most high-clarity polyester bottles do notpossess the necessary dimensional stability to be hot-filled withproduct at temperatures between about 180° F. and 205° F., especiallybetween about 195° F. and 205° F. In particular, at such elevatedtemperature conventional polyester bottles exhibit unacceptableshrinkage and haze. In addition, polyester bottles that packagecarbonated beverages have been known to suffer stress cracking, whichleads to catastrophic failure, or exhibit thermal instability (e.g.,thermal creep), which can result in packaging deformations such as(e.g., fill-line drop, base rocking, and label distortion).

Therefore, there is a need for polyethylene terephthalate resin that issuitable for making both high-clarity, hot-fill bottles that can befilled with product at temperatures between about 180° F. and 205° F.and high-strength, high-clarity bottles that possess improved resistanceto stress cracking and thermal creep.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to providepolyester resin that is capable of being efficiently formed intolow-haze, high-clarity articles.

It is a further object of the present invention to provide apolyethylene terephthalate resin that can be efficiently formed intohigh-clarity polyester preforms and bottles.

It is a further object of the present invention to provide apolyethylene terephthalate resin that can be efficiently formed intohigh-strength, high-clarity polyester bottles suitable for carbonatedsoft drinks

It is a further object of the present invention to provide apolyethylene terephthalate resin that can be formed over a widestretch-blow molding process window into high-strength, high-claritypolyester bottles.

It is a further object of the present invention to provide high-claritypolyester bottles that possess superior strength properties with respectto stress cracking and thermal stability.

It is a further object of the present invention to provide high-claritypreforms that have improved reheating profiles and that can beefficiently formed into hot-fill polyester bottles.

It is a further object of the present invention to provide high-claritypolyester bottles that retain acceptable dimensional stability uponbeing filled with product at temperatures between about 195° F. and 205°F.

It is a further object of the present invention to provide methods forefficiently forming titanium-catalyzed polyethylene terephthalateresins, preforms, and bottles.

It is a further object of the present invention to provide methods forefficiently forming titanium-catalyzed polyethylene terephthalate resinsvia melt-phase polycondensation.

It is a further object of the present invention to provide apolyethylene terephthalate resin that can be used to make fibers, yarns,and fabrics.

The foregoing, as well as other objectives and advantages of theinvention and the manner in which the same are accomplished, is furtherspecified within the following detailed description and its accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 illustrate differential scanning calorimetry thermal analysesperformed on a titanium-catalyzed polyethylene terephthalate resinhaving an intrinsic viscosity of 0.78 dL/g and being modified with 1.6mole percent diethylene glycol and 1.5 mole percent isophthalic acid.

FIGS. 3-4 illustrate differential scanning calorimetry thermal analysesperformed on an antimony-catalyzed polyethylene terephthalate resinhaving an intrinsic viscosity of 0.78 dL/g and being modified with 1.6mole percent diethylene glycol and 1.5 mole percent isophthalic acid.

FIGS. 5-6 illustrate differential scanning calorimetry thermal analysesperformed on a titanium-catalyzed polyethylene terephthalate resinhaving an intrinsic viscosity of 0.78 dL/g and being modified with 1.6mole percent diethylene glycol and 2.4 mole percent isophthalic acid.

FIGS. 7-8 illustrate differential scanning calorimetry thermal analysesperformed on an antimony-catalyzed polyethylene terephthalate resinhaving an intrinsic viscosity of 0.78 dL/g and being modified with 1.6mole percent diethylene glycol and 2.4 mole percent isophthalic acid.

FIG. 9 illustrates percent haze versus preform thickness as measured ina step parison for titanium-catalyzed and antimony-catalyzedpolyethylene terephthalate resins.

FIG. 10 illustrates percent haze versus preform thickness as measured ina step parison formed from titanium-catalyzed polyethylene terephthalateresins that include pentaerythritol according to the present inventionand antimony-catalyzed polyethylene terephthalate resins that excludebranching agent.

FIG. 11 illustrates the theoretical loss of intrinsic viscosity ofpolyethylene terephthalate having an intrinsic viscosity of 0.63 dL/g asa function of the concentration of the reactive carrier at variousmolecular weights.

FIG. 12 illustrates the theoretical loss of intrinsic viscosity ofpolyethylene terephthalate having an intrinsic viscosity of 0.45 dL/g asa function of the concentration of the reactive carrier at variousmolecular weights.

FIGS. 13-14 illustrates the absorbance (cm⁻¹) of a representativepolyethylene terephthalate unenhanced by heat-up rate additives.

FIG. 15 compares caustic stress cracking (95-percent confidenceintervals) for 20-oz. carbonated soft drink bottles formed fromtitanium-catalyzed and antimony-catalyzed polyethylene terephthalateresins (both with and without pentaerythritol branching agent) asdetermined according to the accelerated testing methodology of theInternational Society of Beverage Technologists (ISBT).

FIG. 16 compares caustic stress cracking (95-percent confidenceintervals) for 20-oz. carbonated soft drink bottles formed fromtitanium-catalyzed and antimony-catalyzed polyethylene terephthalateresins (both with and without pentaerythritol branching agent) uponprolonged exposure to less severe conditions than those of ISBT'saccelerated testing methodology.

FIG. 17 compares caustic stress cracking (95-percent confidenceintervals) for two-liter carbonated soft drink bottles formed fromtitanium-catalyzed polyethylene terephthalate resins that includepentaerythritol and antimony-catalyzed polyethylene terephthalate resinsthat exclude branching agent as determined according to ISBT'saccelerated testing methodology.

FIG. 18 compares caustic stress cracking for 20-oz. carbonated softdrink bottles formed from titanium-catalyzed polyethylene terephthalateresins that include pentaerythritol and antimony-catalyzed polyethyleneterephthalate resins that exclude branching agent upon prolongedexposure to less severe conditions than those of ISBT's acceleratedtesting methodology.

FIG. 19 compares percent high-pressure expansion (95-percent confidenceintervals) for 20-oz. carbonated soft drink bottles formed fromtitanium-catalyzed and antimony-catalyzed polyethylene terephthalateresins (both with and without pentaerythritol branching agent).

FIG. 20 compares thermal stability (i.e., percent height change) for20-oz. carbonated soft drink bottles formed from titanium-catalyzed andantimony-catalyzed polyethylene terephthalate resins (both with andwithout pentaerythritol branching agent).

FIG. 21 compares thermal stability (i.e., percent neck diameter change)for 20-oz. carbonated soft drink bottles formed from titanium-catalyzedand antimony-catalyzed polyethylene terephthalate resins (both with andwithout pentaerythritol branching agent).

FIG. 22 compares thermal stability (i.e., percent height and neckdiameter change) for 20-oz. carbonated soft drink bottles formed fromtitanium-catalyzed polyethylene terephthalate resins that includepentaerythritol and antimony-catalyzed polyethylene terephthalate resinsthat exclude branching agent.

FIG. 23 compares thermal stability (i.e., fill line change and finalbase clearance) for 20-oz. carbonated soft drink bottles formed fromtitanium-catalyzed polyethylene terephthalate resins that includepentaerythritol and antimony-catalyzed polyethylene terephthalate resinsthat exclude branching agent.

FIG. 24 depicts the free-blow results for preforms formed fromtitanium-catalyzed and antimony-catalyzed polyethylene terephthalateresins (both with and without pentaerythritol branching agent).

DETAILED DESCRIPTION

The invention is a slow-crystallizing polyethylene terephthalate resin.As herein disclosed, the polyethylene terephthalate resins of thepresent invention possess a significantly higher heating crystallizationexotherm peak temperature (T_(CH)) as compared with those ofconventional antimony-catalyzed polyethylene terephthalate resins. Thiselevated heating crystallization exotherm temperature delays the onsetof crystallization. Accordingly, the polyethylene terephthalate resinsof the present invention are especially useful for making hot-fillbottles having exceptional clarity and shrinkage properties.

In one aspect, the invention is a polyethylene terephthalate resinpossessing a heating crystallization exotherm peak temperature (T_(CH))of more than about 140° C., an absorbance (A) of at least about 0.18cm⁻¹ at an wavelength of 1100 nm or 1280 nm, and an L* value of morethan about 70 as classified in the CIE L*a*b* color space.

In another aspect, the invention is a polyethylene terephthalate resinthat includes at least 2 parts per million (ppm)—and typically less than50 ppm—of elemental titanium and less than about 6 mole percentcomonomer substitution. This titanium-catalyzed polyethyleneterephthalate resin is especially useful in containers, sheets, films,and packaging, but may be used for fibers, yarns, and fabrics as well.

In yet another aspect, the invention is a polyethylene terephthalatepreform that is useful for enhanced heat-set bottles. The polyethyleneterephthalate preform possesses a heating crystallization exotherm peaktemperature (T_(CH)) of more than about 140° C., an absorbance (A) of atleast about 0.18 cm⁻¹ at an wavelength of 1100 nm or 1280 nm, and an L*value of more than about 70 as classified in the CIE L*a*b* color space.

In yet another aspect, the invention is a polyester preform that can beformed into a high-clarity bottle that has excellent, low shrinkageproperties. The preform typically includes less than about six (6) molepercent comonomer substitution and has an intrinsic viscosity of lessthan about 0.86 dL/g. In a related aspect, the invention is ahigh-clarity, hot-fill bottle formed from the preform.

In yet another aspect, the invention is a polyester preform that can beformed into a high-clarity bottle having excellent thermal expansionproperties. The preform typically includes less than about six (6) molepercent comonomer substitution and has an intrinsic viscosity of betweenabout 0.78 and 0.86 dL/g. In a related aspect, the invention is ahigh-strength, high-clarity carbonated soft drink bottle formed from thepreform. The carbonated soft drink bottle is capable of withstandinginternal pressures of about 60 psig.

In yet another aspect, the invention is a titanium-based catalyst systemthat facilitates the melt phase polymerization of these polyethyleneterephthalate resins.

In yet another aspect, the invention is a catalyst system of Group I andGroup II metals that facilitates the solid state polymerization (SSP) ofpolyethylene terephthalate resins. The SSP catalyst system may includealkali earth metals (i.e., Group I metals), alkaline earth metals (i.e.,Group II metals), or both.

In yet another aspect, the invention embraces methods for making suchpolyester resins, preforms, and bottles, as well as other articles(e.g., films and 1+ millimeter sheets). In this regard, the methodgenerally includes reacting a terephthalate component and a diolcomponent (i.e., a terephthalate moiety and a diol moiety) in thepresence of a titanium catalyst to form polyethylene terephthalateprecursors, which are then polymerized via melt phase polycondensationto form polymers of polyethylene terephthalate of desired molecularweight. During polycondensation, which is usually enhanced by catalysts,ethylene glycol is continuously removed to create favorable reactionkinetics.

Those having ordinary skill in the art will appreciate that mostcommercial polyethylene terephthalate polymers are, in fact, modifiedpolyethylene terephthalate polyesters. Indeed, the polyethyleneterephthalate resins described herein are typically modifiedpolyethylene terephthalate polyesters. In this regard, the modifiers inthe terephthalate component and the diol component (i.e., theterephthalate moiety and the diol moiety) are typically randomlysubstituted in the resulting polyester composition.

As noted, for many applications the titanium-catalyzed polyethyleneterephthalate resin possesses low comonomer substitution. Thepolyethylene terephthalate generally includes less than about 6 molepercent comonomer substitution. The polyethylene terephthalate typicallyincludes less than 5 mole percent comonomer substitution or more than 2mole percent comonomer substitution, or both (i.e., between about 2 and5 mole percent).

Although higher comonomer substitution disrupts crystallization, therebyimproving clarity, heat-setting is enhanced at lower comonomersubstitution. Thus, for resins used in making hot-fill bottles, thepolyethylene terephthalate typically includes between about 3 and 4 molepercent comonomer substitution. For example, in one such embodiment themodified polyethylene terephthalate is composed of about a 1:1 molarratio of (1) a diacid component of 2.4 mole percent isophthalic acidwith the remainder terephthalic acid, and (2) a diol component of 1.6mole percent diethylene glycol and the remainder ethylene glycol.

As used herein, the term “diol component” refers primarily to ethyleneglycol, although other diols (e.g., diethylene glycol) may be used aswell.

The term “terephthalate component” broadly refers to diacids anddiesters that can be used to prepare polyethylene terephthalate. Inparticular, the terephthalate component mostly includes eitherterephthalic acid or dimethyl terephthalate, but can include diacid anddiester comonomers as well. In other words, the “terephthalatecomponent” is either a “diacid component” or a “diester component.”

The term “diacid component” refers somewhat more specifically to diacids(e.g., terephthalic acid) that can be used to prepare polyethyleneterephthalate via direct esterification. The term “diacid component,”however, is intended to embrace relatively minor amounts of diestercomonomer (e.g., mostly terephthalic acid and one or more diacidmodifiers, but optionally with some diester modifiers, too).

Similarly, the term “diester component” refers somewhat morespecifically to diesters (e.g., dimethyl terephthalate) that can be usedto prepare polyethylene terephthalate via ester exchange. The term“diester component,” however, is intended to embrace relatively minoramounts of diacid comonomer (e.g., mostly dimethyl terephthalate and oneor more diester modifiers, but optionally with some diacid modifiers,too).

Moreover, as used herein, the term “comonomer” is intended to includemonomeric and oligomeric modifiers (e.g., polyethylene glycol).

The diol component can include other diols besides ethylene glycol(e.g., diethylene glycol, polyalkylene glycols, 1,3-propane diol,1,4-butane diol, 1,5-pentanediol, 1,6-hexanediol, propylene glycol,1,4-cyclohexane dimethanol (CHDM), neopentyl glycol,2-methyl-1,3-propanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol,adamantane-1,3-diol,3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane,and isosorbide), or the terephthalate component, in addition toterephthalic acid or its dialkyl ester (i.e., dimethyl terephthalate),can include modifiers such as isophthalic acid or its dialkyl ester(i.e., dimethyl isophthalate), 2,6-naphthalene dicarboxylic acid or itsdialkyl ester (i.e., dimethyl 2,6 naphthalene dicarboxylate), adipicacid or its dialkyl ester (i.e., dimethyl adipate), succinic acid, itsdialkyl ester (i.e., dimethyl succinate), or its anhydride (i.e.,succinic anhydride), or one or more functional derivatives ofterephthalic acid. The terephthalate component may also include phthalicacid, phthalic anhydride, biphenyl dicarboxylic acid, cyclohexanedicarboxylic acid, anthracene dicarboxylic acid, adamantane1,3-dicarboxylic acid, glutaric acid, sebacic acid, or azelaic acid.

For polyethylene terephthalate bottle resins according to the presentinvention, isophthalic acid and diethylene glycol are the preferredmodifiers. Those having ordinary skill in the art will appreciate thatas a modifier, cyclohexane dimethanol efficiently suppresses polymercrystallinity, but has poor oxygen permeability properties.

For polyethylene terephthalate fiber resins according to the presentinvention, no comonomer substitution is necessary, but where employed,typically includes diethylene glycol or polyethylene glycol.

It will be understood that diacid comonomer should be employed when theterephthalate component is mostly terephthalic acid (i.e., a diacidcomponent), and diester comonomer should be employed when theterephthalate component is mostly dimethyl terephthalate (i.e., adiester component).

It will be further understood by those having ordinary skill in the artthat to achieve the polyester compositions of the present invention amolar excess of the diol component is reacted with the terephthalatecomponent (i.e., the diol component is present in excess ofstoichiometric proportions).

In reacting a diacid component and a diol component via a directesterification reaction, the molar ratio of the diacid component and thediol component is typically between about 1.0:1.0 and 1.0:1.6.Alternatively, in reacting a diester component and a diol component viaan ester interchange reaction, the molar ratio of the diester componentand the diol component is typically greater than about 1.0:2.0.

The diol component usually forms the majority of terminal ends of thepolymer chains and so is present in the resulting polyester compositionin slightly greater fractions. This is what is meant by the phrases“about a 1:1 molar ratio of a terephthalate component and a diolcomponent,” “about a 1:1 molar ratio of a diacid component and a diolcomponent,” and “about a 1:1 molar ratio of the diester component andthe diol component,” each of which may be used to describe the polyestercompositions of the present invention.

The titanium-catalyzed polyethylene terephthalate resin is typicallycomposed of about a 1:1 molar ratio of a diacid component and a diolcomponent. For titanium-catalyzed polyethylene terephthalate resin foruse as high-clarity hot-fill bottles and high-strength carbonated softdrink bottles, the diacid component typically includes at least about 94mole percent terephthalic acid (e.g., terephthalic acid and isophthalicacid) and the diol component includes at least about 94 mole percentethylene glycol (e.g., ethylene glycol and diethylene glycol). Thosehaving ordinary skill in the art will understand that correspondingranges apply to polyethylene terephthalate resins composed of diester(i.e., mostly dimethyl terephthalate) and diol moieties.

In an exemplary embodiment, the polyethylene terephthalate includesabout a 1:1 molar ratio of (1) a diacid component of mostly terephthalicacid and (2) a diol component of between about 1 and 2 mole percentdiethylene glycol, between about 1 and 3 mole percent 1,4-cyclohexanedimethanol, and the remainder ethylene glycol (e.g., about 3-4 diolcomonomer substitution). In an alternative exemplary embodiment, thepolyethylene terephthalate includes about a 1:1 molar ratio of (1) adiester component of mostly dimethyl terephthalate and (2) a diolcomponent of between about 1 and 2 mole percent diethylene glycol,between about 1 and 3 mole percent 1,4-cyclohexane dimethanol, and theremainder ethylene glycol.

The titanium-catalyzed polyethylene terephthalate resin according to thepresent invention generally possesses an exemplary intrinsic viscosityof more than about 0.70 dL/g or less than about 0.90 dL/g, or both(i.e., between about 0.70 dL/g and 0.90 dL/g). Those having ordinaryskill in the art will appreciate, however, that during injection moldingoperations polyester resins tend to lose intrinsic viscosity (e.g., anintrinsic viscosity loss of about 0.02-0.06 dL/g from chip to preform).

Alternatively, the polyethylene terephthalate may have an intrinsicviscosity of more than about 0.78 dL/g (e.g., 0.81 dL/g) or less thanabout 0.86 dL/g (e.g., 0.84 dL/g), or both (i.e., between about 0.78dL/g and 0.86 dL/g).

For polyester resins that are capable of forming high-clarity, hot-fillpreforms and bottles according to the present invention, thepolyethylene terephthalate generally has an intrinsic viscosity of lessthan about 0.86 dL/g, such as between about 0.72 dL/g and 0.84 dL/g).For example, the polyethylene terephthalate has an intrinsic viscosityof more than about 0.68 dL/g or less than about 0.80 dL/g, or both(i.e., between about 0.68 dL/g and 0.80 dL/g). Typically, thepolyethylene terephthalate has an intrinsic viscosity of more than about0.75 dL/g as well (i.e., between about 0.75 dL/g and 0.78 dL/g or, morelikely, between about 0.78 dL/g and 0.82 dL/g). For preforms used tomake hot-fill bottles, heat-setting performance diminishes at higherintrinsic viscosity levels and mechanical properties (e.g., stresscracking, drop impact, and creep) decrease at lower intrinsic viscositylevels (e.g., less than 0.6 dL/g).

For polyester resins that are capable of forming high-strength,high-clarity carbonated soft drink preforms and bottles according to thepresent invention, the polyethylene terephthalate typically has anintrinsic viscosity of more than about 0.72 dL/g or less than about 0.88dL/g, or both (i.e., between about 0.72 dL/g and 0.84 dL/g). Thepolyethylene terephthalate typically has an intrinsic viscosity of morethan about 0.78 dL/g, and most typically, an intrinsic viscosity ofbetween about 0.80 dL/g and 0.84 dL/g.

As noted, mechanical properties (e.g., stress cracking, drop impact, andcreep) decrease at lower intrinsic viscosity levels (e.g., less than 0.6dL/g). Accordingly, bottle resins according to the present inventiontypically have an intrinsic viscosity of 0.60 dL/g or more. In thisregard, for water bottles and other applications that do not demand highstrength (e.g., some sheets and films), the polyethylene terephthalatemay have an intrinsic viscosity of more than about 0.60 dL/g (e.g.,between about 0.60 dL/g and 0.65 dL/g), typically more than about 0.72dL/g or less than about 0.78 dL/g (e.g., 0.74-0.76 dL/g), or both (i.e.,between about 0.72 dL/g and 0.78 dL/g).

For polyester fibers (and some films) according to the presentinvention, the polyethylene terephthalate typically has an intrinsicviscosity of between about 0.50 dL/g and 0.70 dL/g and typically anintrinsic viscosity between about 0.60 dL/g and 0.65 dL/g (e.g., 0.62dL/g). The polyethylene terephthalate fiber resins are typicallypolymerized only in the melt phase (i.e., the fiber resins usually donot undergo solid state polymerization). More generally, to the extentresins according to the present invention are polymerized only in themelt phase (i.e., no solid state polymerization), such resins maypossess an intrinsic viscosity floor of about 0.50 dL/g.

As used herein, the term “intrinsic viscosity” is the ratio of thespecific viscosity of a polymer solution of known concentration to theconcentration of solute, extrapolated to zero concentration. Intrinsicviscosity, which is widely recognized as standard measurements ofpolymer characteristics, is directly proportional to average polymermolecular weight. See, e.g., Dictionary of Fiber and Textile Technology,Hoechst Celanese Corporation (1990); Tortora & Merkel, Fairchild'sDictionary of Textiles (7^(th) Edition 1996).

Intrinsic viscosity can be measured and determined without undueexperimentation by those of ordinary skill in this art. For theintrinsic viscosity values described herein, the intrinsic viscosity isdetermined by dissolving the copolyester in orthochlorophenol (OCP),measuring the relative viscosity of the solution using a SchottAutoviscometer (AVS Schott and AVS 500 Viscosystem), and thencalculating the intrinsic viscosity based on the relative viscosity.See, e.g., Dictionary of Fiber and Textile Technology (“intrinsicviscosity”).

In particular, a 0.6-gram sample (+/−0.005 g) of dried polymer sample isdissolved in about 50 ml (61.0-63.5 grams) of orthochlorophenol at atemperature of about 105° C. Fibrous samples are typically cut intosmall pieces, whereas chip samples are ground. After cooling to roomtemperature, the solution is placed in the viscometer at a controlled,constant temperature, (e.g., between about 20° and 25° C.), and therelative viscosity is measured. As noted, intrinsic viscosity iscalculated from relative viscosity.

As noted, the titanium-catalyzed polyethylene terephthalate resintypically includes between about 2 ppm and 50 ppm of elemental titanium.Typically, the resin includes less than 25 ppm of elemental titanium(e.g., between about 2 and 20 ppm). More typically, the resin includesat least about 5 ppm of elemental titanium or less than about 15 ppm ofelemental titanium, or both (i.e., between about 5 and 15 ppm, such asabout 10 ppm). The titanium catalyst is typically a titanate, such astitanium diisopropoxide bis(acetyl-acetonate) or tetrabutyl titanate. Insome embodiments, the resin includes more than about 10 ppm of elementaltitanium (e.g., between about 10 and 25 ppm).

Those having ordinary skill in the art will appreciate that germanium isan excellent polyethylene terephthalate catalyst. Germanium, however, isprohibitively expensive and so is disfavored in the production ofcommercial polyesters.

Accordingly, the present resin reduces costs by including less thanabout 20 ppm of elemental germanium, typically less than about 15 ppm ofelemental germanium, and more typically less than about 10 ppm ofelemental germanium. Typically, the titanium-catalyzed polyethyleneterephthalate resins include less than 5 ppm of elemental germanium andmore typically less than about 2 ppm of elemental germanium. In manyinstances, the titanium-catalyzed polyethylene terephthalate resins areessentially free of elemental germanium. In other instances, however,the titanium-catalyzed polyethylene terephthalate resins include atleast about two ppm of elemental germanium.

Those having ordinary skill in the art will further appreciate thattitanium-catalyzed polyester resins possess lower rates ofcrystallization as compared with conventional antimony-catalyzedpolyester resins. The titanium-catalyzed polyethylene terephthalateresins of the present invention thus possess lower crystallinity thanotherwise identical antimony-catalyzed polyethylene terephthalateresins. Without being bound to a particular theory, it is believed thattitanium is a poor nucleator as compared with antimony. Consequently,the titanium-catalyzed polyethylene terephthalate resins of the presentinvention possess lower crystallization rates as compared withantimony-catalyzed polyesters. As will be understood by those havingordinary skill in art, this permits preforms according to the presentinvention to be blow molded into high-clarity bottles.

Accordingly, the present resin includes less than about 100 ppm ofelemental antimony, typically less than about 75 ppm of elementalantimony, and more typically less than about 50 ppm of elementalantimony. Typically, the titanium-catalyzed polyethylene terephthalateresins include less than 25 ppm of elemental antimony and more typicallyless than about 10 ppm of elemental antimony. In many instances, thetitanium-catalyzed polyethylene terephthalate resins are essentiallyfree of elemental antimony. Antimony-free polyethylene terephthalateresins may be desirable as antimony is considered a heavy metal. Inother instances, however, the titanium-catalyzed polyethyleneterephthalate resins include at least about 10 ppm of elementalantimony.

FIGS. 1-8 depict differential scanning calorimetry (DSC) thermalanalyses performed on both titanium-catalyzed and antimony-catalyzedpolyester resins at an intrinsic viscosity of about 0.78 dL/g. FIGS. 1-4compare titanium-catalyzed and antimony-catalyzed polyethyleneterephthalate resins having about 3 mole percent comonomer substitution.FIGS. 5-8 compare the titanium-catalyzed and antimony-catalyzedpolyethylene terephthalate resins including about 4 mole percentcomonomer substitution.

The differential scanning calorimetry was performed by (1) holding amodified polyethylene terephthalate sample for one minute at 30 degreesCelsius; (2) heating the sample from 30 degrees Celsius to 280 degreesCelsius at 10 degrees Celsius per minute; (3) holding the sample at 280degrees Celsius for two minutes; and (4) cooling the sample from 280degrees to 30 degrees Celsius at 10 degrees Celsius per minute. FIGS. 1,3, 5, and 7 correspond to the heating of amorphous polymer and FIGS. 2,4, 6, and 8 correspond to the cooling of the same polymer from the meltphase.

FIGS. 1-2 show that at the comonomer substitution of about 3 percent(i.e., 1.6 mole percent diethylene glycol and 1.5 mole percentisophthalic acid substitution), the titanium-catalyzed polyethyleneterephthalate polyester possesses a heating crystallization exothermpeak temperature (T_(CH)) of 144.2° C., crystalline melting peaktemperature (T_(M)) of 253.2° C., and a cooling crystallization exothermpeak temperature (T_(CC)) of 186.8° C.

FIGS. 3-4 show that at the comonomer substitution of about 3 percent(i.e., 1.6 mole percent diethylene glycol and 1.5 mole percentisophthalic acid substitution), antimony-catalyzed polyethyleneterephthalate polyester possesses a heating crystallization exothermpeak temperature (T_(CH)) of 130.6° C., crystalline melting peaktemperature (T_(M)) of 251.5° C., and a cooling crystallization exothermpeak temperature (T_(CC)) of 191.0° C.

FIGS. 5-6 show that at the comonomer substitution of about 4 percent(i.e., 1.6 mole percent diethylene glycol and 2.4 mole percentisophthalic acid substitution), the titanium-catalyzed polyethyleneterephthalate polyester possesses a heating crystallization exothermpeak temperature (T_(CH)) of 146.3° C., crystalline melting peaktemperature (T_(M)) of 250.0° C., and a cooling crystallization exothermpeak temperature (T_(CC)) of 181.3° C.

FIGS. 7-8 show that at the comonomer substitution of about 4 percent(i.e., 1.6 mole percent diethylene glycol and 2.4 mole percentisophthalic acid substitution), antimony-catalyzed polyethyleneterephthalate polyester possesses a heating crystallization exothermpeak temperature(T_(CH)) of 131.5° C., crystalline melting peaktemperature (T_(M)) of 250.9° C., and a cooling crystallization exothermpeak temperature (T_(CC)) of 187.8° C.

As FIGS. 1-8 illustrate, the titanium-catalyzed polyethyleneterephthalate resins of the present invention possess a significantlyhigher heating crystallization exotherm peak temperature (T_(CH)) ascompared with antimony-catalyzed polyethylene terephthalate. Thosehaving ordinary skill in the art will appreciate that this higherheating crystallization exotherm temperature is especially desirable inblow molding operations as it delays the onset of crystallization,thereby facilitating the formation of high-clarity bottles.

Accordingly, at a heating rate of 10° C. per minute as measured bydifferential scanning calorimetry, the polyethylene terephthalate resinhas a heating crystallization exotherm peak temperature (T_(CH)) of morethan about 140° C. and typically more than about 142° C. (e.g., between143° C. and 153° C.). Indeed, the polyethylene terephthalate resin canpossess a crystallization exotherm peak temperature (T_(CH)) of 155° C.or more. Those having ordinary skill in the art will recognize thatheating crystallization exotherm peak temperature (T_(CH)) is determinedon a non-crystalline polyethylene terephthalate resin.

The polyethylene terephthalate resin also has a crystalline melting peaktemperature (T_(M)) of at least about 240° C., typically at least about245° C., and more typically at least about 250° C. Those having ordinaryskill in the art will understand that the melting point is largelydependent on comonomer content.

Moreover, at a cooling rate of 10° C. per minute as measured bydifferential scanning calorimetry, the polyethylene terephthalate resinhas a cooling crystallization exotherm peak temperature (T_(CC)) of lessthan about 190° C. and typically less than about 185° C. In someinstances, the polyethylene terephthalate resin has a coolingcrystallization exotherm peak temperature (T_(CC)) of less than about180° C.

The titanium-catalyzed polyethylene terephthalate resin of the presentinvention possesses high clarity as compared with an otherwise identicalantimony-catalyzed polyethylene terephthalate resin. In this regard,FIG. 9 depicts percent haze versus preform thickness as measured in astep parison for titanium-catalyzed and antimony-catalyzed polyethyleneterephthalate resins at an intrinsic viscosity of about 0.78 dL/g andeither 3 mole percent comonomer substitution (i.e., 1.6 mole percentdiethylene glycol and 1.5 mole percent isophthalic acid substitution) or4 mole percent comonomer substitution (i.e., 1.6 mole percent diethyleneglycol and 2.4 mole percent isophthalic acid substitution). FIG. 9illustrates that at a given comonomer substitution, thetitanium-catalyzed polyethylene terephthalate resin possessessubstantially lower haze as compared with its correspondingantimony-catalyzed polyethylene terephthalate resin. Those havingordinary skill in the art will appreciate that, in general, highercomonomer substitution disrupts polymer crystallinity, thereby reducingpreform and bottle haze.

As measured in a step parison, the polyethylene terephthalate of thepresent invention typically possesses less than about 20 percenthaze—preferably less than about 15 percent haze—at a thickness of morethan about 6 mm and less than about 5 percent haze at a thickness ofmore than about 4 mm. Moreover, as measured in a step parison, thepolyethylene terephthalate typically possesses less than about 10percent haze at a thickness of more than about 4.5 mm, and sometimes ata thickness of more than 5.5 mm (e.g., less than about 10 percent hazeat a thickness of between 4.5 and 6.0 mm). In some formulations, thepolyethylene terephthalate possesses less than about 20 percent haze ata thickness of between 5.5 and 6.5 mm as measured in a step parison. Asdepicted in FIG. 9, the polyethylene terephthalate can possess less thanabout 50 percent haze at a thickness of more than about 7 mm.

Likewise, as measured in two-liter polyester bottle having a sidewallthickness of 0.014 inch (0.35 mm), the polyethylene terephthalate of thepresent invention typically possesses less than about 15 percentsidewall haze, typically less than about 10 percent sidewall haze, andmore typically less than about 5 percent sidewall haze.

FIG. 10 compares percent haze as measured in step parisons formed fromtitanium-catalyzed polyethylene terephthalate resins that includepentaerythritol according to the present invention and step parisonsformed from antimony-catalyzed polyethylene terephthalate resins thatexclude branching agent. FIG. 10 illustrates the superior clarity ofpolyethylene terephthalate resins of the present invention versusantimony-catalyzed polyethylene terephthalate resins that, except forcatalyst and branching agent differences, possess comparableformulations (i.e., between 5 and 6 mole percent comonomer, namely 3.0mole percent isophthalic acid and 2.4 mole percent diethylene glycol,and 2.8 mole percent isophthalic acid and 3.0 mole percent diethyleneglycol, respectively).

Those having ordinary skill in the art understand that polyethyleneterephthalate preforms and bottles must possess excellent color (i.e.,not too yellow). In this regard, excessive levels of titanium catalystcan cause the polyethylene terephthalate resin to appear yellow.

Color differences are commonly classified according to the L*a*b* colorspace of the Commission Internationale l′Eclairage (CIE). The threecomponents of this system consist of L*, which describes luminosity on ascale of 0-100 (i.e., 0 is black and 100 is white), a*, which describesthe red-green axis (i.e., positive values are red and negative valuesare green), and b*, which describes the yellow-blue axis (i.e., positivevalues are yellow and negative values are blue). For characterizingpolyester resins, L* and b* values are of particular interest.

In this regard, it is preferred that polyester color be measured afterpolymerization in the solid phase. After solid state polymerization, thepolyethylene terephthalate resin of the present invention possesses anL* value (i.e., luminosity) of more than about 70, typically more thanabout 75 (e.g., 77), and in some instances more than about 80 asclassified in the CIE L*a*b* color space. That said, the polyethyleneterephthalate resin can possess an L* value as low as about 65 and stillbe suitable for carbonated soft drink bottles. In addition, thepolyethylene terephthalate resin typically possesses a b* color value ofless than about 2 (e.g., less than about 0) as classified by the CIEL*a*b* color space. Typically, the polyethylene terephthalate resinpossesses a b* color value of between about −3 and 2 as classified bythe CIE L*a*b* color space.

Those having ordinary skill in the art will appreciate that althoughcolor can be measured in polyester preforms and polyester bottles, coloris often more conveniently measured in polyester pellets or polyesterplaques. (As set forth herein, the term “pellets” is used generally torefer to chips, pellets, and the like.)

Those having ordinary skill in the art will know that polyethyleneterephthalate resins are typically formed into pellets before undergoingcrystallization and/or solid state polymerization. As a result, aftercrystallization (and/or solid state polymerization) but prior to polymerprocessing (e.g., injection molding), the polyethylene terephthalateresins of the present invention are crystalline pellets; it is preferredthat color be measured in that form. In this regard and unless otherwiseindicated (e.g., such as with respect to non-crystalline plaques), theCIE L*a*b* color space values reported herein for the polyethyleneterephthalate resins of the present invention relate to crystallinepolyethylene terephthalate pellets.

CIE L*a*b* color space values for the crystalline polyethyleneterephthalate pellets were determined using a HunterLab LabScan XEspectrophotometer (illuminant/observer: D65/10°; 45°/0° geometry;perfect reflectance diffuser NBS78; standard color tile LX16697). Thosehaving ordinary skill in the art will appreciate that crystallinepolyester pellets are translucent and so are typically measured viareflectance using a clear sample cup. In this regard, test procedures(e.g., standards and calibrations) appropriate for measuring colorproperties of crystalline polyester in various forms (e.g., pellets) arereadily available to and within the understanding of those havingordinary skill in the art.

As described herein, the polyethylene terephthalate resin of the presentinvention can be injection molded into preforms, which in turn may beblow molded into bottles. Measuring color in preforms and bottles,however, can be awkward. Consequently, it is preferred that preforms andbottles be formed into plaques to facilitate comparative colormeasurements. In this regard, the polyethylene terephthalate preformsand bottles according to the present invention are ground, melted at280° C., and then injected into a cold mold to form standard, threemillimeter (3 mm) non-crystalline polyester test plaques. The CIE L*a*b*color space values reported herein for the polyethylene terephthalatepreforms and bottles of the present invention relate to measurementstaken upon such standard test plaques.

As these standard test plaques are formed from either polyester preformsor polyester bottles, the constituent polyesters may possess unfavorableheat histories. Those having ordinary skill in the art will appreciatethat this may somewhat degrade the constituent polyesters. In thisregard, it has been observed that injection molding preforms from thecrystalline polyethylene terephthalate pellets of the present invention(and thereafter forming standard test plaques) can introduce someyellowing (i.e., the b* color value increases slightly).

Accordingly, the polyethylene terephthalate preforms and bottles of thepresent invention typically possess a b* color value of less than about4—preferably less than about 2 (e.g., less than about 0)—as classifiedby the CIE L*a*b* color space. Most typically, the polyethyleneterephthalate preforms and bottles possess a b* color value of betweenabout −3 and 3 as classified by the CIE L*a*b* color space.

Like the aforementioned crystalline polyethylene terephthalate pellets,however, the polyethylene terephthalate preforms and bottles of thepresent invention possess an L* value of more than about 70, typicallymore than about 75 (e.g., 77), and preferably more than about 80 (e.g.,83 or more) as classified in the CIE L*a*b* color space.

As noted, these CIE L*a*b* color space values for preforms and bottlesrefer to measurements from standard, non-crystalline polyester testplaques.

CIE L*a*b* color space values for the three-millimeter, non-crystallinepolyethylene terephthalate test plaques were determined using aHunterLab LabScan XE spectrophotometer (illuminant/observer: D65/10°;diffuse 8° standard; transmittance port). Those having ordinary skill inthe art will appreciate that non-crystalline polyester plaques areessentially transparent and so are measured by transmittance. In thisregard, test procedures (e.g., standards and calibrations) appropriatefor measuring color properties of non-crystalline polyester in variousforms are readily available to and within the understanding of thosehaving ordinary skill in the art.

Such color has been achieved according to the present invention byincluding between about 10 and 50 ppm of elemental cobalt, typicallybetween about 15 and 40 ppm of elemental cobalt, and most typicallybetween 20 and 30 ppm of elemental cobalt. In the absence of cobalt, thepolyethylene terephthalate resin of the present invention tends toappear yellowish. The present polyethylene terephthalate resin possessesexcellent color without the inclusion of colorants, apart from a cobaltcatalyst. (Those having ordinary skill in the art will appreciate thatcobalt not only provides catalytic activity, but also imparts bluecoloration to the polyethylene terephthalate resin.)

Where the polyethylene terephthalate resin is intended for packaging(e.g., polyester preforms and bottles), it may include a heat-up rateadditive. In this regard, the heat-up rate additive is present in theresin in an amount sufficient to improve the resin's reheating profile.As will be understood by those having ordinary skill in the art, aheat-up rate additive helps preforms absorb energy during preformreheating processes. In reheating preforms, the inside of the preformshould be at least as warm as the outside of the preform as the insideundergoes more stretching during blow molding.

To those having ordinary skill in the art, it is counterintuitive to usea slow-crystallizing polyethylene terephthalate resin in the productionof heat-set bottles. For example, U.S. Pat. No. 6,699,546 (Tseng)teaches the inclusion of nucleation agents to accelerate the rate ofresin crystallization for improved heat-set bottles.

As explained previously, slow-crystallizing polyethylene terephthalateresins possess a significantly higher heating crystallization exothermpeak temperature (T_(CH)) as compared with those of antimony-catalyzedpolyethylene terephthalate resins. The objective of the heat-settingprocess is to maximize bottle crystallinity and stress relaxation whilemaintaining clarity. It would seem that a slower crystallizing resinwould have inferior heat-setting capability. Consequently, including aheat-up rate additive to achieve higher preform temperatures—and thuspromoting crystallinity in the slower crystallizing resin—would seem tobe of no practical benefit. Under such circumstances, those havingordinary skill in the art would not expect to achieve improved bottleproperties (e.g., clarity and shrinkage).

For example, consider a bottle preform made from a slow-crystallizingpolyethylene terephthalate resin (e.g., the titanium-catalyzed polyesterresins herein disclosed) that further includes a heat-up rate additive.As noted, compared with antimony, titanium slows the onset of thermalcrystallization in the preform as the preform is heated. The heat-uprate additive, however, causes the preform to absorb more energy and,therefore, to reach significantly higher temperatures before the onsetof crystallization. Thus, good preform clarity is maintained even atelevated preform temperatures.

Surprisingly, the inventors have discovered that modifying aslow-crystallizing polyester resin to include sufficient heat-up rateadditive to enhance the resin's reheating profile actual improves blowmolding performance and bottle properties, such as shrinkage. Theincreased preform temperature in the blow molding and heat-settingprocesses promotes bottle crystallization and stress relaxation whileproducing bottles having clarity superior to those of antimony-catalyzedpolyethylene terephthalate resins.

In one embodiment, the heat-up rate additive is a carbon-based heat-uprate additive. Carbon-based heat-up rate additive is typically presentin the polyethylene terephthalate resin in an amount less than about 25ppm. More typically, carbon-based heat-up rate additive is present inthe polyethylene terephthalate resin in an amount between about 4 and 16ppm (e.g., 8-12 ppm), most typically in an amount between about 6 and 10ppm. Suitable carbon-based additives include carbon black, activatedcarbon, and graphite. For example, satisfactory carbon black heat-uprate additives are disclosed in U.S. Pat. No. 4,408,004 (Pengilly),which is hereby incorporated entirely by reference.

In another embodiment, the heat-up rate additive is a metal-containingheat-up rate additive. Metal-containing heat-up rate additive istypically present in the polyethylene terephthalate resin in an amountbetween about 10 and 300 ppm, more typically in an amount greater thanabout 75 ppm (e.g., between about 150 and 250 ppm). Suitablemetal-containing heat-up rate additives include metals, metal oxides,minerals (e.g., copper chromite spinels), and dyes. For example,satisfactory inorganic black pigments and particles are disclosed inU.S. Pat. No. 6,503,586 (Wu), which is hereby incorporated entirely byreference.

Preferred metal-containing heat-up rate additives are tungsten-basedadditives, such as tungsten metal or tungsten carbide. In this regard,tungsten-containing heat-up rate additive powders typically have anaverage particle size of between about 0.7 and 5.0 microns, moretypically between about 0.9 and 2.0 microns.

As will be understood by those familiar with this art, particle size istypically measured by techniques based on light scattering. Particlesizes and distributions are often characterized according to ASTM B330-2(“Standard Test Method for Fisher Number of Metal Powders and RelatedCompounds”).

Other preferred metal-containing heat-up rate additives aremolybdenum-based additives, especially molybdenum sulfide (MoS₂). Inthis regard, molybdenum sulfide has outstanding heat absorptionproperties, so it can be included in somewhat lesser quantities (e.g.,5-100 ppm) as compared with other metal-containing heat-up rateadditives.

The most preferred heat-up rate additives are natural spinels andsynthetic spinels. Spinels are typically included in the polyethyleneterephthalate resin in an amount between about 10 and 100 ppm (e.g.,between about 15 and 25 ppm). Particularly outstanding spinel pigmentsare copper chromite black spinel and chrome iron nickel black spinel.

These spinels are disclosed in commonly assigned U.S. patent applicationSer. No. 09/247,355, for Thermoplastic Polymers with Improved InfraredReheat Properties, filed Feb. 10, 1999, now abandoned, and itsdivisions: U.S. patent application Ser. No. 09/973,499, published asU.S. Patent Publication 2002/0011694 A1 on Jan. 31, 2002; U.S. patentapplication Ser. No. 09/973,520, published as U.S. Patent Publication2002-0027314 A1 on Mar. 7, 2002: and U.S. patent application Ser. No.09/973,436, published as U.S. Patent Publication 2002-0033560 A1 on Mar.21, 2002. Each of these patent applications and patent publications ishereby incorporated entirely by reference.

The heat-up rate of a polyethylene terephthalate preform can bedescribed by surface temperature measurements at a fixed location on apreform for a particular bottle production rate.

In polyethylene terephthalate bottle production, polyethyleneterephthalate bottle preforms are reheated by passing the preformsthrough a reheat oven of a blow molding machine. The reheat ovenconsists of a bank of quartz lamps (3,000 and 2,500 watt lamps) thatemit radiation mostly in the infrared range. The ability of the preformto absorb this radiation and convert it into heat, thereby allowing thepreform to reach the orientation temperature for blow molding, isimportant for optimum bottle performance and efficient production.Important bottle properties for bottle performance are materialdistribution, orientation, and sidewall crystallinity.

Preform reheat temperature is important for control of these properties.Depending on the kind of bottle being produced, the preform reheattemperature is typically in the range of 30-50° C. above the glasstransition temperature (T_(g)) of polyethylene terephthalate. The reheattemperature depends on the application (e.g., hot-filled beverage bottleor carbonated soft drink bottles). The rate at which a preform can bereheated to the orientation temperature is important for optimal bottleperformance in high-speed, polyethylene terephthalate blow-moldingmachines, such as those manufactured by Sidel, Inc. (LeHavre, France).This is especially true for heat-set bottles that are intended forfilling with hot liquids in excess of 185° F. In heat-set bottleproduction, the preform is reheated rapidly to as high a temperature aspossible. This maximizes crystallization upon blow molding and avoidsthermal crystallization in the preform. Those having ordinary skill inthe art will appreciate that such thermal crystallization can causeunacceptable haze as a result of spherulitic crystallization.

In view of the importance of preform reheating, the following method hasbeen used to assess the reheat characteristics of polyethyleneterephthalate preforms. As initial matter, this test method analyzes thereheat characteristics of polyethylene terephthalate preforms (orresins) by forming test parisons from one or more polyethyleneterephthalate resin formulations. It is the test parisons (i.e.,stepped-core preforms)—not commercial preforms—that are actually tested:

First, the subject resin is formed into a 5.25-inch test parison havinga weight of 47 grams, an overall diameter of 1.125 inches, and a0.75-inch neck finish. To form such a test parison, a polyethyleneterephthalate resin is dried at 350° F. for four hours in a desiccantdryer. The dried resin is introduced into a 4-ounce Newburyinjection-molding machine. The resin is kneaded and melted to provide amolten resin with a temperature in the range of 500° F. to 520° F. Then,the molten resin is injected into a preform mold designed for atwo-liter carbonated soft drink bottle. The total cycle time is 60seconds, including injection, pack, and cooling time. The mold iscontinuously chilled to 45° F. These injection molding conditions give aclear test parison that is predominately amorphous (i.e., less thanabout 4 percent crystallinity).

The reheat performance of the 5.25-inch test parison is tested using aSidel SBO1 laboratory blow molding machine. This machine has one reheatoven with a bank of up to ten independently adjustable quartz lamps, aninfrared camera to measure preform surface temperature, a transfer armform the oven to blow mold, one blow mold, and a bottle transfer armextending from the blow mold to the machine exit.

In this test method, the SBO1 laboratory blow molding machinecontinuously produces polyethylene terephthalate bottles at a rate of1,000 bottles per hour using eight quartz lamps. The oven has powercontrol that can be adjusted as a percentage of the overall oven poweroutput. Likewise, each lamp can be adjusted as a percentage of theindividual lamp power output.

To determine the reheat characteristics of a 5.25-inch parison, themachine is set up at a bottle production rate of 1,000 bottles per hour.A standard resin is selected to produce a test parison. Then, thereheating profile for this test parison is established. The reheatingprofile is used to produce commercially acceptable bottles at an overallpower output of 80 percent. Thereafter, the percentage of the overallpower is varied between 65 and 90 percent and the surface temperature isrepeatedly measured at a fixed location on the test parison.

The reheat performance of the 5.25-inch test parison is consistentlymeasured 1.4-inches below the support ring of the neck finish. At thislocation, (i.e., 1.4 inches below the support ring), the test parisonhas a wall thickness of 0.157-inch.

EXAMPLE 1

A two-liter polyethylene terephthalate bottle test parison was producedfrom a standard resin (i.e., Wellman's PermaClear® HP806 polyesterresin). This test parison required eight reheat zones for production ofa straight-wall, two-liter bottle. At an overall oven power percentageof 80 percent, the reheating profile for this PermaClear® HP806 testparison is shown in Table 1:

TABLE 1 Heating Zones Power output (%) 1 74 2 60 3 55 4 55 5 55 6 68 786 8 74

After establishing this reheating profile, two samples were preparedfrom an antimony-catalyzed polyethylene terephthalate resin having lessthan about 6 mole percent comonomer substitution. One sample includedabout 11 ppm of a carbon-based heat-up rate additive (Resin A) and theother sample, a control, included no heat-up rate additive (Resin B).Besides the presence of a heat-up rate additive, Resin A and Resin Bwere otherwise identical. The reheat performance (i.e., via surfacetemperature measurements) for both Resin A and Resin B were thenmeasured (in five-percent increments) at the overall oven power outputsof between 65 and 90 percent:

TABLE 2 Overall Oven Resin A Resin B Power Output (%) (surface temp. °C.) (surface temp. ° C.) 65 87.3 81.0 70 92.0 85.0 75 95.8 87.5 80 100.592.0 85 107.0 97.3 90 113.0 101.0

Table 2 demonstrates that improved preform reheat performance isachieved as a result of the inclusion of a heat-up rate additive.

Accordingly, to improve preform reheat performance, the polyethyleneterephthalate resin of the present invention may include a heat-up rateadditive in a concentration sufficient for an aforementioned 5.25-inchtest parison to achieve reheating surface temperatures that, as measured1.4 inches below the support ring of the neck finish where the wallthickness is 0.157 inch, are at least about 4° C. higher thancorresponding reheating temperatures achievable by an otherwiseidentical 5.25-inch test parison (i.e., without a heat-up rate additive)as measured on a Sidel SB01 laboratory blow-molding machine operating ata production rate of 1,000 bottles per hour and using eight lamps atoverall power levels of 65 percent, 70 percent, 75 percent, 80 percent,85 percent, and 90 percent, respectively. The difference in respectivereheating surface temperatures is more preferably at least about 7° C.and most preferably at least about 10° C.

In another embodiment, the polyethylene terephthalate resin of thepresent invention includes a heat-up rate additive in a concentrationsufficient for an aforementioned 5.25-inch test parison to achieve anaverage reheating surface temperature that, as measured 1.4 inches belowthe support ring of the neck finish where the wall thickness is 0.157inch, is at least about 5° C. higher—preferably 10° C. higher—than theaverage reheating temperature achievable by an otherwise identical5.25-inch test parison (i.e., without a heat-up rate additive) asmeasured on a Sidel SB01 laboratory blow-molding machine operating at aproduction rate of 1,000 bottles per hour and using eight lamps atoverall power levels between about 65 and 90 percent.

Alternatively, the intrinsic heat-up rate of polyester resin can bedescribed by its characteristic absorption of energy. In this regard,electromagnetic radiation exists across several spectra. For example,electromagnetic radiation can be measured in the ultraviolet, visible,near-infrared, and infrared ranges. The visible light spectrum fallsbetween about 430 nm and 690 nm. This spectrum is bounded by ultravioletradiation and infrared radiation, respectively. With respect to thereheating profile of polyester, near infrared radiation (NIR) is ofparticular interest.

More specifically, the intrinsic heat-up rate of polyester resin can becharacterized by its absorbance of electromagnetic radiation. Absorbanceis described by Beer's Law, which is expressed as equation 1:

A=ε·l·c   Eq. 1

wherein

A is absorbance of electromagnetic radiation by a sample,

ε is the proportionality constant of the sample (i.e., “molarabsorptivity”),

l is the path length of the sample through which electromagneticradiation must pass, and

c is the concentration of the sample (typically measured inmoles/liter).

With respect to polyester resin, however, equation 1 can be simplified.For a particular polyester resin, molar absorptivity and sampleconcentration can be ignored. Moreover, a linear relationship existsbetween absorbance and path length (i.e., sample thickness). Thus, for apolymer resin, absorbance (A) can be calculated from transmittance (T)as follows:

A=log(100)−log(% T)   Eq. 2

Equation 2 is further simplified as expressed in equation 3:

A=2−log(% T)   Eq. 3

In brief, transmittance is the ratio of the intensity of theelectromagnetic radiation that passes through the polymer resin to theintensity of the electromagnetic radiation that enters the polymerresin. As reported herein, absorbance, which is calculated from therelationship expressed in equation 3, describes the electromagneticradiation that a non-crystalline polyethylene terephthalate resin failsto transmit.

As noted previously, the polyethylene terephthalate resins of thepresent invention generally possess absorbance (A) of at least about0.18 cm⁻¹ at a wavelength of 1100 nm or at a wavelength of 1280 nm.Moreover, the present polyethylene terephthalate resins typicallypossess absorbance (A) of at least about 0.20 cm⁻¹ at a wavelength of1100 nm or at a wavelength of 1280 nm, preferably possess absorbance (A)of at least about 0.24 cm⁻¹ at a wavelength of 1100 nm or at awavelength of 1280 nm absorbance (A), and more preferably possessabsorbance (A) of at least about 0.28 cm⁻¹ at a wavelength of 1100 nm orat a wavelength of 1280 nm absorbance (A).

Those having ordinary skill in the art will understand that as usedherein the disjunctive (i.e., “or”) includes the conjunctive (i.e.,“and”). Moreover, with respect to the present disclosure, absorbance isreported for non-crystalline polyester.

In its most preferred embodiments, the polyethylene terephthalate resinspossess an absorbance (A) of at least about 0.25 cm⁻¹ at a wavelength of1100 nm or at a wavelength of 1280 nm, and preferably an absorbance (A)of at least about 0.30 cm⁻¹ at a wavelength of 1100 nm or at awavelength of 1280 nm. In some embodiments, the polyethyleneterephthalate resins possess an absorbance (A) of at least about 0.30cm⁻¹ at a wavelength of 1100 nm or at a wavelength of 1280 nm, and inparticular embodiments an absorbance (A) of at least about 0.40 cm⁻¹ ata wavelength of 1100 nm or at a wavelength of 1280 nm. Thesepolyethylene terephthalate resins can be achieved by including betweenabout 10 and 100 ppm of a copper chromite black spinel.

In this regard, absorbance was determined within the visible and NIRspectra for both a non-crystalline unenhanced polyethylene terephthalateresin (PET) and an otherwise identical polyethylene terephthalate resin,albeit enhanced with 22 ppm of a copper chromite black spinel heat-uprate additive (PET/spinel). Table 3 reports absorbance for thesepolyester resins at 550 nm, 700 nm, 1100 nm, and 1280 nm:

TABLE 3 Absorbance (cm⁻¹) 550 nm 700 nm 1100 nm 1280 nm PET 0.209 0.1700.145 0.144 PET/spinel 0.399 0.374 0.314 0.314

The wavelengths reported in Table 3 are meaningful. In particular, 550nm falls near the midpoint of the visible light spectrum and 700 nmfalls near the upper end of the visible spectrum. Moreover, as depictedin FIGS. 13-14, the absorbance for unenhanced polyethylene terephthalateis nearly flat (i.e., the slope is about 0) at 1100 nm and 1280 nm,thereby facilitating repeatable measurements at these wavelengths withinthe NIR spectrum.

To enhance color, it is preferred that heat-up rate additives promotethe absorption of more NIR radiation and lesser amounts of visibleradiation. This can be described by the absorption ratio as hereindefined. In brief, for a polyester resin, the absorption ratio is simplythe antilog of the absorbance at a first wavelength divided by theantilog of the absorbance at a second wavelength. This is expressed inequation 4:

absorption ratio=(antilog A ₁)/(antilog A ₂)   Eq. 4

wherein

A₁ is absorbance at a first wavelength, and

A₂ is absorbance at a second wavelength.

With respect to absorption ratio, the first wavelength typically fallswithin the NIR spectrum (e.g., 1280 nm) and the second wavelengthtypically falls within the visible spectrum (e.g., 550 nm). Table 4indicates that the polyethylene terephthalate enhanced with 22 ppm ofcopper chromite spinel has similar absorption selectivity to that of theunenhanced polyethylene terephthalate, despite having significantlyhigher absorbance (e.g., absorbance greater than 0.30 cm⁻¹ at both 1100nm and 1280 nm).

TABLE 4 Absorption Ratio 1100:550 1280:550 1100:700 1280:700 PET 0.8640.862 0.945 0.943 PET/spinel 0.822 0.822 0.871 0.871

The present polyethylene terephthalate resins preferably possess a1100:550 absorption ratio of at least about 70 percent or a 1280:550absorption ratio of at least about 70 percent. More preferably, thepresent polyethylene terephthalate resins possess a 1100:550 absorptionratio of at least about 75 percent or a 1280:550 absorption ratio of atleast about 75 percent. In some embodiments, the present polyethyleneterephthalate resins preferably possess a 1100:550 absorption ratio ofat least about 80 percent or a 1280:550 absorption ratio of at leastabout 80 percent.

Similarly, the present polyethylene terephthalate resins preferablypossess a 1100:700 absorption ratio of at least about 85 percent or a1280:700 absorption ratio of at least about 85 percent. In someembodiments, the present polyethylene terephthalate resins possess a1100:700 absorption ratio of at least about 90 percent (e.g., 95 percentor more) or a 1280:700 absorption ratio of at least about 90 percent(e.g., 95 percent or more).

With respect to the present disclosure, absorbance was determined forthree millimeter (3 mm), non-crystalline polyester plaques using a FossSeries 6500 Transport Analyzer. This instrument is typical of thosecapable of measuring transmittance in the visible and NIR spectra inthat instrumentation factors (e.g., lamp, detector, vibration, and airfiltration) can affect absorbance measurements. Of course, the use ofappropriate standards and calibrations is within the understanding ofthose having ordinary skill in the art.

To control for testing variability, the absorbance data must benormalized at an incident wavelength of 2132 nm such that thecorresponding absorbance is 0.473 mm⁻¹ ¹ (i.e., 4.73 cm⁻¹). At thiswavelength additives have modest effect on absorbance fornon-crystalline polyethylene terephthalate.

The inventors have also considered the effect of sample reflectance, buthave determined that it may be disregarded when determining absorbanceof polyester resins. In brief, reflectance is radiation that has beenscattered from the surface of a solid, liquid, or gas. Reflectedelectromagnetic energy is expressed in relation to the energy absorbedand energy transmitted as expressed in equation 5:

I _(O) =I _(A) +I _(T) +I _(R)   Eq. 5

wherein

I_(O) is incident energy,

I_(A) is absorbed energy,

I_(T) is transmitted energy, and

I_(R) is reflected energy.

As described previously, absorbance is derived from the transmittance.See equation 3. Reflectance is generally not measured, and so theinventors have considered whether ignoring reflectance introducessubstantial errors in the determination of absorbance.

In this regard, it would seem that a polyester plaque having a polishedsurface would have a higher reflectance than would a polyester plaquehaving a “matte” or other non-reflective finish. If reflectance is notconsidered, increasing reflectance would seem to decrease transmittance.In accordance with equation 3, this would have the effect of falselyincreasing calculated absorbance.

Therefore, to reduce absolute reflectance and control reflectancevariability, the polyester plaques should have a consistent finishacross batches (i.e., semi-glossy). It is believed that by controllingthe physical properties of the polyester plaques in this way,reflectance becomes negligible in assessing absorbance and absorptionratio.

Those having ordinary skill in the art will know that there are twoconventional methods for forming polyethylene terephthalate. Thesemethods are well known to those skilled in the art.

One method employs a direct esterification reaction using terephthalicacid and excess ethylene glycol. In this technique, the aforementionedstep of reacting a terephthalate component and a diol component includesreacting terephthalic acid and ethylene glycol in a heatedesterification reaction to form monomers and oligomers of terephthalicacid and ethylene glycol, as well as a water byproduct. To enable theesterification reaction to go essentially to completion, the water mustbe continuously removed as it is formed. The monomers and oligomers aresubsequently catalytically polymerized via polycondensation (i.e., meltphase and/or solid state polymerization) to form polyethyleneterephthalate polyester. As noted, ethylene glycol is continuouslyremoved during polycondensation to create favorable reaction kinetics.

The other method involves a two-step ester exchange reaction andpolymerization using dimethyl terephthalate and excess ethylene glycol.In this technique, the aforementioned step of reacting a terephthalatecomponent and a diol component includes reacting dimethyl terephthalateand ethylene glycol in a heated, catalyzed ester exchange reaction(i.e., transesterification) to form bis(2-hydroxyethyl)-terephthalatemonomers, as well as methanol as a byproduct.

To enable the ester exchange reaction to go essentially to completion,the methanol must be continuously removed as it is formed. Thebis(2-hydroxyethyl)terephthalate monomer product is then catalyticallypolymerized via polycondensation (i.e., melt phase and/or solid statepolymerization) to produce polyethylene terephthalate polymers. Theresulting polyethylene terephthalate polymers are substantiallyidentical to the polyethylene terephthalate polymer resulting fromdirect esterification using terephthalic acid, albeit with some minorchemical differences (e.g., end group differences).

Polyethylene terephthalate polyester may be produced in a batch process,where the product of the ester interchange or esterification reaction isformed in one vessel and then transferred to a second vessel forpolymerization. Generally, the second vessel is agitated and thepolymerization reaction is continued until the power used by theagitator reaches a level indicating that the polyester melt has achievedthe desired intrinsic viscosity and, thus, the desired molecular weight.More commercially practicable, however, is to carry out theesterification or ester interchange reactions, and then thepolymerization reaction as a continuous process. The continuousproduction of polyethylene terephthalate results in greater throughput,and so is more typical in large-scale manufacturing facilities.

In the present invention, the direct esterification reaction ispreferred over the older, two-step ester exchange reaction. Directesterification terephthalic acid is not only more economical but oftenyields polyethylene terephthalate resins having better color.

In this regard and as noted, the direct esterification technique reactsterephthalic acid and ethylene glycol along with no more than 6 molepercent diacid and diol modifiers to form low molecular weight monomers,oligomers, and water. In particular, both titanium and cobalt catalystspreferably are added during esterification as this has been found toimprove the color of the resulting polyethylene terephthalate resins.The polyethylene terephthalate resin may optionally include othercatalysts, such as aluminum-based catalysts, manganese-based catalysts,or zinc-based catalysts.

More specifically, the titanium catalyst is introduced in an amountsufficient for the final polyethylene terephthalate resin to includebetween about 2 and 50 ppm of elemental titanium. Likewise, the cobaltcatalyst is introduced in an amount sufficient for the finalpolyethylene terephthalate resin to include between about 10 and 50 ppmof elemental cobalt. To prevent process disruptions (e.g., cloggedpiping), it is recommended that the titanium and cobalt catalysts beintroduced into an esterification vessel by a different delivery means.

The inclusion of a titanium or cobalt catalyst increases the rate ofesterification and polycondensation and, hence, the production of thepolyethylene terephthalate resins. These catalysts, however, willeventually degrade the polyethylene terephthalate polymer. For example,degradation may include polymer discoloration (e.g., yellowing),acetaldehyde formation, or molecular weight reduction. To reduce theseundesirable effects, stabilizing compounds can be employed to sequester(“cool”) the catalysts. The most commonly used stabilizers containphosphorus, typically in the form of phosphates and phosphites.

Accordingly, the present resin typically includes a phosphorusstabilizer. In this regard, the phosphorus stabilizer may be introducedinto the polyethylene terephthalate polymers such that the phosphorus ispresent in the resulting resin, on an elemental basis, in an amount lessthan about 100 ppm (e.g., between about 15 and 75), typically in anamount less than about 60 ppm (e.g., between about 10 and 20 ppm), andmore typically in an amount between about 2 and 40 ppm (e.g., betweenabout 5 and 15 ppm). In one exemplary embodiment, the phosphorus ispresent in the resulting resin in an amount less than about 10 ppm(i.e., between about 2 and 10 ppm). In another exemplary embodiment, thephosphorus is present in the resulting resin in an amount greater thanabout 15 ppm (e.g., between about 20 and 50 ppm). The phosphorusstabilizer may be introduced into the melt phase any time afteresterification, but it is typically added to the melt afterpolycondensation is essentially complete.

Although adding a phosphorus stabilizer to the polymer melt in a batchreactor is a relatively simple process, numerous problems arise if thestabilizers are added in the continuous production of polyethyleneterephthalate. For example, while early addition of the stabilizerprevents discoloration and degradation of the polyester, it also causesreduced production throughput (i.e., decreases polycondensation reactionrates). Moreover, phosphorus stabilizers are typically dissolved inethylene glycol, the addition of which further slows the polymerizationprocess. Consequently, early addition of the stabilizer in thepolymerization process requires an undesirable choice between productionthroughput and thermal stability of the polymer. As used herein,“thermal stability” refers to a low rate of acetaldehyde generation(e.g., less than about 5 ppm), low discoloration, and retention ofmolecular weight following subsequent heat treatment or otherprocessing.

Later addition of the phosphorus stabilizer may provide insufficientopportunity for the stabilizer to fully blend with the polymer.Consequently, the phosphorus stabilizer may not prevent degradation anddiscoloration of the polyester. In addition, adding phosphorusstabilizer during polymer processing is often inconvenient and does notprovide economies of scale.

U.S. Pat. No. 5,376,702 for a Process and Apparatus for the Direct andContinuous Modification of Polymer Melts discloses dividing a polymermelt stream into an unmodified stream and a branch stream that receivesadditives. In particular, a side stream takes a portion of the branchstream to an extruder, where additives are introduced. Such techniques,however, are not only complicated, but also costly, requiring a screwextruder and melt piping to process additives. Consequently, sucharrangements are inconvenient and even impractical where total additiveconcentrations are low (e.g., less than one weight percent).

Certain problems associated with late addition of stabilizer areaddressed in U.S. Pat. No. 5,898,058 for a Method of Post-PolymerizationStabilization of High Activity Catalysts in Continuous PolyethyleneTerephthalate Production, which discloses a method of stabilizing highactivity polymerization catalysts in continuous polyethyleneterephthalate production. This patent, which is commonly assigned withthis application, is hereby incorporated entirely herein by reference.

In particular, U.S. Pat. No. 5,898,058 discloses adding a stabilizer,which preferably contains phosphorus, at or after the end of thepolymerization reaction and before polymer processing. This deactivatesthe polymerization catalyst and increases the throughput of thepolyester without adversely affecting the thermal stability of thepolyethylene terephthalate polyester. While a noteworthy improvementover conventional techniques, U.S. Pat. No. 5,898,058 teaches adding thestabilizer without a carrier. Consequently, the addition of solids intothe polymer necessitates the costly use of an extruder.

The aforementioned U.S. application Ser. No. 09/738,150 for Methods ofPost-Polymerization Injection in Continuous Polyethylene TerephthalateProduction, now U.S. Pat. No. 6,599,596, discloses a process for theproduction of high quality polyethylene terephthalate polyester thatimproves upon the stabilizer-addition techniques disclosed by commonlyassigned U.S. Pat. No. 5,898,058.

More specifically, U.S. application Ser. No. 09/738,150 discloses amethod for the late introduction of additives into a process for makingpolyethylene terephthalate. The additives are introduced during, andpreferably after, the polycondensation of polyethylene terephthalatepolymers. In particular, the method employs a reactive carrier that notonly functions as a delivery vehicle for one or more additives, but alsoreacts with the polyethylene terephthalate, thereby binding the carrierin the polyethylene terephthalate resin. Moreover, U.S. application Ser.No. 09/738,150 discloses that this may be achieved using a simplifiedadditive delivery system that does not require the use of an extruder.(U.S. application Ser. No. 09/932,150, for Methods ofPost-Polymerization Extruder Injection in Polyethylene TerephthalateProduction, now U.S. Pat. No. 6,569,991, which is a continuation-in-partof U.S. application Ser. No. 09/738,150, discloses a method for lateadditive introduction at an extruder during a process for makingpolyethylene terephthalate.)

The phosphorus stabilizers herein disclosed can be introduced to thepolyethylene terephthalate polymers directly, as a concentrate inpolyethylene terephthalate, or as a concentrate in a liquid carrier. Thepreferred point of addition in the polyethylene terephthalatepolymerization process is after completion of polycondensation (i.e.,mixed with the molten polymer stream after the final polymerizationvessel).

The phosphorus stabilizer is typically introduced to the polyethyleneterephthalate polymers via a reactive carrier, rather than via an inertcarrier or no carrier at all. The reactive carrier, which preferably hasa molecular weight of more than about 200 g/mol and less than about10,000 g/mol may be introduced during polycondensation, or moretypically, after the polycondensation is complete. In either respect,the reactive carrier should be introduced to the polyethyleneterephthalate polymers in quantities such that bulk polymer propertiesare not significantly affected.

As a general matter, the reactive carrier should make up no more thanabout one weight percent of the polyethylene terephthalate resin.Preferably, the reactive carrier is introduced to the polyethyleneterephthalate polymers in quantities such that its concentration in thepolymer resin is less than about 1,000 ppm (i.e., 0.1 weight percent).Reducing the reactive carrier to quantities such that its concentrationin the polymer resin is less than 500 ppm (i.e., 0.05 weight percent)will further reduce potential adverse effects to bulk polymerproperties.

Most preferably, the reactive carrier has a melting point that ensuresthat it is a liquid or slurry at near ambient temperatures. Near ambienttemperatures not only simplify the unit operations (e.g., extruders,heaters, and piping), but also minimize degradation of the inertparticulate additives. As used herein, the term “near ambient” includestemperatures between about 20° C. and 60° C.

In general, reactive carriers having carboxyl, hydroxyl, or aminefunctional groups are favored. Preferred are polyols, especiallypolyester polyols and polyether polyols, having a molecular weight thatis sufficiently high such that the polyol will not substantially reducethe intrinsic viscosity of the polyethylene terephthalate polymer, and aviscosity that facilitates pumping of the polyol. Polyethylene glycol isa preferred polyol. Other exemplary polyols include functionalpolyethers, such as polypropylene glycol that is prepared from propyleneoxide, random and block copolymers of ethylene oxide and propyleneoxide, and polytetramethylene glycol that is derived from thepolymerization of tetrahydrofuran.

Alternatively, the reactive carrier may include dimer or trimer acidsand anhydrides. In another embodiment, the reactive carrier may possess,in addition to or in place of terminal functional groups, internalfunctional groups (e.g., esters, amides, and anhydrides) that react withthe polyethylene terephthalate polymers. In yet another embodiment, thereactive carrier may include non-functional esters, amides, oranhydrides that is capable of reacting into the polyethyleneterephthalate polymers during solid state polymerization and that willnot cause the polyethylene terephthalate polymers to suffer intrinsicviscosity loss during injection molding processes.

In view of the foregoing, an exemplary method of making thetitanium-catalyzed polyethylene terephthalate resin of the presentinvention includes reacting, in a heated esterification reaction, adiacid moiety that includes at least 94 mole percent terephthalic acidand a diol moiety that includes at least 94 mole percent ethyleneglycol.

For many applications, the diacid and diol modifiers should be includedsuch that the resulting polyethylene terephthalate polymer has less thanabout 6 mole percent comonomer substitution. The diacid component mayinclude between about 1.6 and 2.4 mole percent isophthalic acid with theremainder terephthalic acid, and the diol component of includes 1.6 molepercent diethylene glycol and the remainder ethylene glycol. Forinstance, a polyethylene terephthalate resin that is useful for makinghigh-strength, high-clarity carbonated soft drink preforms and bottlesmay include between about 2 and 3 mole percent isophthalic acid (e.g.,about 2.4 mole percent) and less than about 3 mole percent diethyleneglycol (e.g., less than 2.4 mole percent).

The esterification reaction is catalyzed by both titanium and cobalt toform monomers and oligomers of terephthalic acid and diacid modifiers,and ethylene glycol and diol modifiers, as well as water, which iscontinuously removed as it is formed to enable the esterificationreaction to go essentially to completion. The titanium catalyst and thecobalt catalyst are concurrently introduced in amounts sufficient forthe polyethylene terephthalate resin to include between about 2 and 50ppm (e.g., 5-15 ppm) of elemental titanium and between about 10 and 50ppm of elemental cobalt (e.g., 20-30 ppm).

The monomers and oligomers are then polymerized via melt phasepolycondensation to form polyethylene terephthalate polymers. Aphosphorus stabilizer is then introduced into the polyethyleneterephthalate polymers, preferably using a reactive carrier. As noted,the reactive carrier facilitates uniform blending within the polymermelt. The phosphorus stabilizer is typically introduced into thepolyethylene terephthalate polymers such that the phosphorus is presentin the resulting resin, on an elemental basis, in an amount less thanabout 100 ppm, typically between about 2 and 60 ppm (e.g., between about20 and 50 ppm). The melt phase polycondensation usually continues untilthe polyethylene terephthalate polymers achieve an intrinsic viscositygreater than about 0.55 dL/g, more typically greater than about 0.60dL/g (e.g., greater than about 0.65 dL/g), and perhaps greater thanabout 0.70 dL/g (e.g., greater than about 0.75 dL/g, such as betweenabout 0.78 and 0.86 dL/g).

Thereafter, the polyethylene terephthalate polymers are formed intopellets, which are then polymerized in the solid state to an intrinsicviscosity of greater than about 0.70 dL/g (e.g., greater than about 0.75dL/g) and more typically greater than about 0.80 dL/g (e.g., betweenabout 0.81 and 0.87 dL/g). In some instances, polyethylene terephthalatepolymers can be polymerized in the solid state to an intrinsic viscosityof greater than about 0.85 dL/g or 0.90 dL/g. In many instances, thepolyethylene terephthalate polymers are polymerized in the solid stateto an intrinsic viscosity of less than 0.86 dL/g (e.g., 0.75-0.78 dL/g).

Preferably, the reactive carrier is a polyol (e.g., polyethylene glycol)having a molecular weight that permits the polyol to be pumped at nearambient temperatures (e.g., less than 60° C.) and that is introduced tothe polyethylene terephthalate polymers in quantities such that bulkproperties of the polyethylene terephthalate polymers are notsignificantly affected (e.g., quantities such that its concentration inthe polymers is less than about one weight percent). The polyethyleneterephthalate polymers are then formed into chips (or pellets via apolymer cutter) before being solid state polymerized. Importantly, thepolyol reactive carrier combines with the polyethylene terephthalatepolymer such that it is non-extractable during subsequent processingoperations (e.g., forming polyester preforms or beverage containers).

Other additives can be incorporated via reactive carrier into thepolyethylene terephthalate resins of the present invention. Suchadditives include preform heat-up rate enhancers, friction-reducingadditives, UV absorbers, inert particulate additives (e.g., clays orsilicas), colorants, antioxidants, branching agents, oxygen barrieragents, carbon dioxide barrier agents, oxygen scavengers, flameretardants, crystallization control agents, acetaldehyde reducingagents, impact modifiers, catalyst deactivators, melt strengthenhancers, anti-static agents, lubricants, chain extenders, nucleatingagents, solvents, fillers, and plasticizers.

Late addition is especially desirable where the additives are volatileor subject to thermal degradation. Conventional additive injection priorto polycondensation, such as during an esterification stage in thesynthesis of polyester, or early during the polycondensation stagesubjects additives to several hours of high-temperature (greater than260° C.) and reduced-pressure (less than 10 torr) conditions.Consequently, additives that have significant vapor pressure at theseconditions will be lost from the process. Advantageously, late additionvia reactive carrier significantly reduces the time additives areexposed to high polycondensation temperatures.

As will be understood by those of ordinary skill in the art,macromolecules are considered to be polymers at an intrinsic viscosityof about 0.45 dL/g. This roughly translates to a molecular weight of atleast about 13,000 g/mol. In contrast, the reactive carriers accordingto the present invention have molecular weights that are more than about200 g/mol and less than about 10,000 g/mol. The molecular weight of thereactive carrier is generally less than 6,000 g/mol, typically less than4,000 g/mol, more typically between about 300 and 2,000 g/mol, and mosttypically between about 400 and 1,000 g/mol. As used herein, molecularweight refers to number-average molecular weight, rather thanweight-average molecular weight.

FIGS. 11 and 12 illustrate the theoretical loss of intrinsic viscosityas a function of reactive carrier concentration at several molecularweights. FIG. 11 depicts the impact of the reactive carrier on uponpolyethylene terephthalate having an intrinsic viscosity of 0.63 dL/g.Similarly, FIG. 12 depicts the impact of the reactive carrier on uponpolyethylene terephthalate having intrinsic viscosity of 0.45 dL/g. Notethat at any concentration, the reactive carriers having higher molecularweights have less adverse effect upon intrinsic viscosity of the polymerresin.

In a typical, exemplary process the continuous feed enters the directesterification vessel that is operated at a temperature of between about240° C. and 290° C. and at a pressure of between about 5 and 85 psia forbetween about one and five hours. The esterification reaction, which istypically catalyzed using both titanium and cobalt catalysts, forms lowmolecular weight monomers, oligomers, and water. The water is removed asthe reaction proceeds to drive favorable reaction equilibrium.

Thereafter, the low molecular weight monomers and oligomers arepolymerized via polycondensation to form polyethylene terephthalatepolyester. This polycondensation stage generally employs a series of twoor more vessels and is operated at a temperature of between about 250°C. and 305° C. for between about one and four hours. Thepolycondensation reaction usually begins in a first vessel called thelow polymerizer. The low polymerizer is operated at a pressure range ofbetween about 0 and 70 torr. The monomers and oligomers polycondense toform polyethylene terephthalate and ethylene glycol.

The ethylene glycol is removed from the polymer melt using an appliedvacuum to drive the reaction to completion. In this regard, the polymermelt is typically agitated to promote the escape of the ethylene glycolfrom the polymer melt and to assist the highly viscous polymer melt inmoving through the polymerization vessel.

As the polymer melt is fed into successive vessels, the molecular weightand thus the intrinsic viscosity of the polymer melt increases. Thetemperature of each vessel is generally increased and the pressuredecreased to allow greater polymerization in each successive vessel.

The final vessel, generally called the “high polymerizer,” is operatedat a pressure of between about 0 and 40 torr. Like the low polymerizer,each of the polymerization vessels is connected to a vacuum systemhaving a condenser, and each is typically agitated to facilitate theremoval of ethylene glycol. The residence time in the polymerizationvessels and the feed rate of the ethylene glycol and terephthalic acidinto the continuous process is determined, in part, based on the targetmolecular weight of the polyethylene terephthalate polyester. Becausethe molecular weight can be readily determined based on the intrinsicviscosity of the polymer melt, the intrinsic viscosity of the polymermelt is generally used to determine polymerization conditions, such astemperature, pressure, the feed rate of the reactants, and the residencetime within the polymerization vessels.

Note that in addition to the formation of polyethylene terephthalatepolymers, side reactions occur that produce undesirable by-products. Forexample, the esterification of ethylene glycol forms diethylene glycol,which is incorporated into the polymer chain. As is known to those ofskill in the art, diethylene glycol lowers the softening point of thepolymer. Moreover, cyclic oligomers (e.g., trimer and tetramers ofterephthalic acid and ethylene glycol) may occur in minor amounts. Thecontinued removal of ethylene glycol as it forms in the polycondensationreaction will generally reduce the formation of these by-products.

After the polymer melt exits the polycondensation stage, typically fromthe high polymerizer, phosphorus stabilizer is introduced via a reactivecarrier. Thereafter, the polymer melt is generally filtered andextruded. After extrusion, the polyethylene terephthalate is quenched,typically by spraying with water, to solidify it. The solidifiedpolyethylene terephthalate polyester is cut into chips or pellets forstorage and handling purposes. The polyester pellets typically have anaverage mass of about 15-20 mg. As used herein, the term “pellets” isused generally to refer to chips, pellets, and the like.

Although the prior discussion assumes a continuous production process,it will be understood that the invention is not so limited. Theteachings disclosed herein may be applied to semi-continuous processesand even batch processes.

As will be known to those of skill in the art, the pellets formed fromthe polyethylene terephthalate polymers may be subjected tocrystallization and, if necessary, solid state polymerization toincrease the molecular weight of the polyethylene terephthalate resin.As compared with antimony, for example, titanium is substantially lessactive as an SSP catalyst. Thus, to facilitate the solid phasepolymerization of the polyethylene terephthalate resins, complementarySSP catalysts are introduced to the polymer melt prior to solid phasepolymerization, typically during polycondensation.

Preferred SSP catalysts include Group I and Group II metals. Acetatesalts of Group I and Group II metals (e.g., calcium acetate, lithiumacetate, manganese acetate, potassium acetate, or sodium acetate) orterephthalate salts can increase solid state polymerization rates. TheSSP catalyst is typically introduced in an amount sufficient for thefinal polyethylene terephthalate resin to include between about 10 and70 ppm of the elemental metal.

After solid state polymerization, the polyester chips are then re-meltedand re-extruded to form bottle preforms, which can thereafter be formedinto polyester containers (e.g., beverage bottles). Bottles formed fromthe resins and preforms described herein preferably have sidewall hazeof less than about 15 percent, more preferably less than about 10percent.

Typically, a hot-fill bottle according to the present invention,exhibits an average circumferential dimension change, as measured fromthe bottle shoulder to the bottle base, of less than about 3 percentwhen filled at 195° F. and less than about 5 percent when filled at 205°F. Moreover, such a hot-fill bottle according to the present inventionexhibits a maximum circumferential dimension change from the bottleshoulder to the bottle base of less than about 5 percent—preferably lessthan 4 percent—when the bottle is filled at 195° F. (Such shrinkageproperties are measured on a 24-hour aged bottle.)

As will be understood by those having ordinary skill in the art,polyethylene terephthalate is typically converted into a container via atwo-step process. First, an amorphous bottle preform (e.g., less thanabout 4 percent crystallinity and typically between about 4 and 7 mm inthickness) is produced from bottle resin by melting the resin in anextruder and injection molding the molten polyester into a preform. Sucha preform usually has an outside surface area that is at least an orderof magnitude smaller than the outside surface of the final container.The preform is reheated to an orientation temperature that is typically30° C. above the glass transition temperature (T_(g)).

The reheated preform is then placed into a bottle blow mold and, bystretching and inflating with high-pressure air, formed into a heatedbottle. The blow mold is maintained at a temperature between about 115°C. and 200° C., usually between about 120° C. and 160° C. Those havingordinary skill in the art will recognize that the introduction ofcompressed air into the heated preform effects formation of the heatedbottle. Thus, in one variation, the compressed air is turbulentlyreleased from the bottle by the balayage technique to facilitate coolingof the heated bottle. It is believed that the preforms according to thepresent invention can be blow molded into low-shrinkage bottles usinglower-than-conventional pressure for the compressed air.

With respect to the high-clarity, hot-fill polyester bottle preforms ofthe present invention, after the reheating step, the preforms are blowmolded into low-shrinkage bottles within a cycle time of less than about6 seconds (i.e., at normal production rates).

Those of ordinary skill in the art will understand that any defect inthe preform is typically transferred to the bottle. Accordingly, thequality of the bottle resin used to form injection-molded preforms iscritical to achieving commercially acceptable bottles. Aspects ofinjection-molding preforms and stretch-blow molding bottles arediscussed in U.S. Pat. No. 6,309,718 for Large Polyester Containers andMethod for Making the Same, which is hereby incorporated entirely hereinby reference.

Those of ordinary skill in the art will further appreciate thatbranching agents may be included in small amounts (e.g., less than about2,000 ppm) to increase polymerization rates and improve bottle-makingprocesses. Chain branching agents can be introduced, for example, duringesterification or melt phase polymerization. Typically, less than 0.1mole percent branching agent is included in the polyethyleneterephthalate resins of the present invention.

As used herein, the term “branching agent” refers to a multifunctionalmonomer that promotes the formation of side branches of linked monomermolecules along the main polymer chain. See Odian, Principles ofPolymerization, pp. 18-20 (Second Edition 1981). The chain branchingagent is preferably selected from the group consisting of trifunctional,tetrafunctional, pentafunctional and hexafunctional alcohols or acidsthat will copolymerize with polyethylene terephthalate. As will beunderstood by those skilled in the art, a trifunctional branching agenthas one reactive site available for branching, a tetrafunctionalbranching agent has two reactive sites available for branching, apentafunctional branching agent has three reactive sites available forbranching and a hexafunctional branching agent has four reactive sitesavailable for branching. Further, as used herein, the term “branchingagent” embraces dendrimers (i.e., hyperbranched polymeric macromoleculespossessing a branches-upon-branches structure).

Acceptable chain branching agents include, but are not limited to,trimesic acid (C₆H₃(COOH)₃), pyromellitic acid (C₆H₂(COOH)₄),pyromellitic dianhydride, trimellitic acid, trimellitic anhydride,trimethylol propane (C₂H₅C(CH₂OH)₃), ditrimethylol propane(C₂H₅C(CH₂OH)₂C₂H₄OC(CH₂OH)₂C₂H₅), dipentaerythritol(CH₂OHC(CH₂OH)₂C₂H₄OC(CH₂OH)₂CH₂OH), pentaerythritol (C(CH₂OH)₄),1,2,3,4-butanetetracarboxylic acid, ethoxylated glycerol, ethoxylatedpentaerythritol (3E0/4OH and 15 EO/4OH from Aldrich Chemicals),ethoxylated trimethylol propane (2.5EO/OH and 20EO/3OH from AldrichChemicals), and Lutrol HF-1 (an ethoxylated glycerol from BASF).

Preferred aromatic chain branching agents—aromatic rings appear to curbstress nucleation—include trimellitic acid (TMLA), trimellitic anhydride(TMA), pyromellitic acid (PMLA), pyromellitic dianhydride (PMDA),benzophenone tetracarboxylic acid, benzophenone tetracarboxylicdianhydride, naphthalene tetracarboxylic acid, and naphthalenetetracarboxylic dianhydride, as well as their derivatives:

The inclusion of chain branching agent has been observed to improvebottles formed from the present polyethylene terephthalate resins. FIGS.15-24 show that the inclusion of branching agent seems to improvecertain properties of carbonated soft drink bottles, such as causticstress cracking and high-pressure expansion, as well as various thermalstability characteristics. In this regard, FIGS. 15-24 depicttitanium-catalyzed polyethylene terephthalate resins according to thepresent invention that include about 3.0 mole percent isophthalic acidand 2.4 mole percent diethylene glycol comonomer substitution andantimony-catalyzed polyethylene terephthalate resins that include about2.8 mole percent isophthalic acid and 3.0 mole percent diethylene glycolcomonomer substitution. Unless otherwise noted, the intrinsicviscosities of the titanium-catalyzed and antimony-catalyzedpolyethylene terephthalate resins depicted in FIGS. 15-24 are betweenabout 0.80 dL/g and 0.84 dL/g.

Those having ordinary skill in the art will recognize that a polyesterresin should facilitate efficient forming operations (e.g., injectionmolding and stretch-blow molding). Surprisingly, at a desired molecularweight, polyethylene terephthalate resins that include branching agentyield carbonated soft drink bottles that possess better physicalproperties than do otherwise identical resins that omit branching agent.Of course, such polyethylene terephthalate resins are suitable not onlyfor carbonated soft drink bottles but also other polyester articles thatcould benefit from improved strength (e.g., films, sheets, and othercontainers).

As noted, the polyethylene terephthalate resins of the present inventiontypically include less than about 0.1 mole percent branching agent. Thebranching agent present in the polyethylene terephthalate resins canalso be expressed in terms of “mole-equivalent branches” per mole ofstandardized polymer, which is herein described with respect tounmodified polyethylene terephthalate.

As used herein, the term “mole-equivalent branches” refers to thereactive sites available for chain branching on a molar basis (i.e., thenumber of reactive sites in excess of the two required to form a linearmolecule). For example, as will be appreciated by those having ordinaryskill in the art, a trifunctional branching agent (e.g., trimethylolpropane or trimellitic acid) possesses one reactive site that isavailable for branching. A tetrafunctional branching agent (e.g.,pentaerythritol) possesses two reactive sites that are available forbranching. Similarly, as further examples, a pentafunctional branchingagent and a hexafunctional branching agent can possess three and fourreactive sites, respectively, that are available for branching.

As used herein, the term “standardized polymer” refers to the repeatunit of unmodified polyethylene terephthalate, which has a molecularweight of 192 g/mol. In this regard, it will be understood by thosehaving ordinary skill in the art that, for a given total weight ofpolyethylene terephthalate, comonomer substitution, and branching agent,changing the relative mole fraction and/or molecular weight of thecomonomer modifiers will affect total moles. Consequently, to maintainconsistency across various concentrations and molecular weights ofcomonomer modifiers, the chain branching agent concentration is based onthe repeat unit of unmodified polyethylene terephthalate.

In other words, the weight fraction of branching agent should becalculated as if the polymer is made of only unmodified polyethyleneterephthalate. Consequently, the mole fraction and/or molecular weightof comonomer modifiers can be disregarded in calculating mole-equivalentbranches per mole of standardized polymer.

Accordingly, as will be appreciated by those having ordinary skill inthe art, a polyethylene terephthalate resin of the present inventionthat includes less than about 0.1 mole percent of a trifunctional chainbranching agent (i.e., providing one available chain branching reactivesite) can be characterized as a polyethylene terephthalate resin thatincludes branching agent in an amount less than about 0.1 percentmole-equivalent branches per mole of standardized polymer as hereindefined.

Likewise, as herein defined, a polyethylene terephthalate resin of thepresent invention that includes less than about 0.1 mole percent of atetrafunctional chain branching agent (i.e., providing two availablechain branching reactive sites), can be characterized as a polyethyleneterephthalate resin that includes branching agent in an amount less thanabout 0.2 percent mole-equivalent branches per mole of standardizedpolymer.

Similarly, as herein defined, a polyethylene terephthalate resin of thepresent invention that includes less than about 0.1 mole percent of apentafunctional chain branching agent (i.e., providing three availablechain branching reactive sites), can be characterized as a polyethyleneterephthalate resin that includes branching agent in an amount less thanabout 0.3 percent mole-equivalent branches per mole of standardizedpolymer.

Finally, as herein defined, a polyethylene terephthalate resin of thepresent invention that includes less than about 0.1 mole percent of ahexafunctional chain branching agent (i.e., providing four availablechain branching reactive sites), can be characterized as a polyethyleneterephthalate resin that includes branching agent in an amount less thanabout 0.4 percent mole-equivalent branches per mole of standardizedpolymer.

To illustrate this relationship (i.e., mole-equivalent branches per moleof standardized polymer), assume 1000 grams of starting materials—about175 ppm pentaerythritol, which has a molecular weight of 136.15 g/mol,and the remainder polyethylene terephthalate. This is equivalent toabout 0.175 gram pentaerythritol, or 0.0013 moles of pentaerythritol,and 999.825 grams polyethylene terephthalate, or 5.21 moles polyethyleneterephthalate repeat units. The mole fraction of pentaerythritolrelative to the polyethylene terephthalate is, therefore, about 0.025mole percent (i.e., 0.00025-0.0013 moles of pentaerythritol 5.21 molespolyethylene terephthalate). As noted, pentaerythritol has two availablechain branching reactive sites. Thus, the mole-equivalent branches permole of unmodified polyethylene terephthalate is about 0.050 percent(i.e., 0.00050 mole-equivalent branches per mole of standardizedpolymer.)

Exemplary polyethylene terephthalate resins of the present invention caninclude, among other illustrative concentrations, chain branching agentin an amount of less than about 0.4 percent mole-equivalent branches permole of standardized polymer as defined herein; less than about 0.3percent mole-equivalent branches per mole of standardized polymer asdefined herein; less than about 0.2 percent mole-equivalent branches permole of standardized polymer as defined herein; less than about 0.14percent mole-equivalent branches per mole of standardized polymer asdefined herein; less than about 0.1 percent mole-equivalent branches permole of standardized polymer as defined herein; less than about 0.08percent mole-equivalent branches per mole of standardized polymer asdefined herein; less than about 0.075 percent mole-equivalent branchesper mole of standardized polymer as defined herein; less than about 0.06percent mole-equivalent branches per mole of standardized polymer asdefined herein; less than about 0.05 percent mole-equivalent branchesper mole of standardized polymer as defined herein; and less than about0.04 percent mole-equivalent branches per mole of standardized polymeras defined herein.

Other exemplary embodiments of the invention include polyethyleneterephthalate resins that incorporate chain branching agent in an amountranging from about 0.02 to about 0.2 percent mole-equivalent branchesper mole of standardized polymer as defined herein; from about 0.04 toabout 0.2 percent mole-equivalent branches per mole of standardizedpolymer as defined herein; from about 0.08 to about 0.2 percentmole-equivalent branches per mole of standardized polymer as definedherein; from about 0.03 to about 0.14 percent mole-equivalent branchesper mole of standardized polymer as defined herein; from about 0.025 toabout 0.1 percent mole-equivalent branches per mole of standardizedpolymer as defined herein; from about 0.03 to about 0.08 percentmole-equivalent branches per mole of standardized polymer as definedherein; from about 0.025 to about 0.075 percent mole-equivalent branchesper mole of standardized polymer as defined herein; from about 0.05 toabout 0.075 percent mole-equivalent branches per mole of standardizedpolymer as defined herein; from about 0.025 to about 0.05 percentmole-equivalent branches per mole of standardized polymer as definedherein; from about 0.04 to about 0.05 percent mole-equivalent branchesper mole of standardized polymer as defined herein; from about 0.01 toabout 0.04 percent mole-equivalent branches per mole of standardizedpolymer as defined herein, among other concentrations; and from about0.02 to about 0.03 percent mole-equivalent branches per mole ofstandardized polymer as defined herein, among other concentrations.

The weight fraction corresponding to mole-equivalent branches per moleof standardized polymer can be estimated for any branching agent usingthe following equation:

branching agent (ppm)=(MEB÷CBRS)·(BAMW÷SPMW)·10⁶, wherein

MEB=mole-equivalent branches per mole of standardized polymer

CBRS=number of available chain branching reactive sites

BAMW=molecular weight of the branching agent (g/mol)

SPMW=192 g/mol—molecular weight of the standardized polymer (i.e.,unmodified polyethylene terephthalate).

Thus, for example, pentaerythritol that is present in an amount betweenabout 0.0004 and 0.00075 mole-equivalent branches per mole ofstandardized polymer (i.e., between about 0.04 and 0.075 percentmole-equivalent branches per mole) is equivalent to a weight fraction ofbetween about 140 and 270 ppm when based on the standardized polymer ofunmodified polyethylene terephthalate (i.e., having a repeat unitmolecular weight of about 192 g/mol). This exemplary amount ofpentaerythritol has been observed to improve the properties ofcarbonated soft drink bottles formed from the polyethylene terephthalateresins of the present invention.

As noted, trifunctional branching agent (e.g., trimethylolpropane—MW=134.17 g/mol, or trimellitic acid—MW=210.15 g/mol) possessesone branching site and tetrafunctional branching agent (e.g.,pentaerythritol—MW=136.15 g/mol) possesses two branching sites.

Consequently, for trimethylol propane, 0.1 mole percent branching agent(i.e., about 700 ppm) converts to 0.1 percent mole-equivalent branchesper mole of standardized polymer, and for trimellitic acid, 0.1 molepercent branching agent (i.e., about 1,100 ppm) likewise converts to 0.1percent mole-equivalent branches per mole of standardized polymer (i.e.,a 1× conversion). For pentaerythritol, in contrast, 0.1 mole percentbranching agent (i.e., about 700 ppm) converts to 0.2 percentmole-equivalent branches per mole of standardized polymer (i.e., a 2×conversion).

Thus, by way of comparison, pentaerythritol at 0.1 percentmole-equivalent branches per mole of standardized polymer converts toabout 350 ppm. Stated otherwise, 350 ppm pentaerythritol has about thesame branching efficacy as 700 ppm trimethylol propane or 1,100 ppmtrimellitic acid.

It will be appreciated by those of skill in the chemical arts that ifthe mole-equivalent branches were not referenced to a mole ofstandardized polymer, a chain branching agent concentration (e.g., lessthan 0.4 percent mole-equivalent branches per mole of polyester) couldtranslate to a slightly higher or lower weight fraction, (i.e., ppm),depending on the mole fraction and/or average molecular weight of thecomonomer modifiers. By employing unmodified polyethylene terephthalateas the standardized polymer, however, pentaerythritol at about 0.05percent mole-equivalent branches per mole of standardized polymer isequivalent to a weight fraction of about 177 ppm, regardless of the molefraction and/or molecular weight of the comonomer modifiers.

This application incorporates entirely by reference the followingcommonly assigned patents, each of which discusses stoichiometric molarratios with respect to reactive end groups (i.e., “mole-equivalentbranches”): U.S. Pat. No. 6,623,853, for Polyethylene Glycol ModifiedPolyester Fibers and Method for Making the Same; U.S. Pat. No.6,582,817, for Nonwoven Fabrics Formed from Polyethylene Glycol ModifiedPolyester Fibers and Method for Making the Same; U.S. Pat. No.6,509,091, for Polyethylene Glycol Modified Polyester Fibers; U.S. Pat.No. 6,454,982, for Method of Preparing Polyethylene Glycol ModifiedPolyester Filaments; U.S. Pat. No. 6,399,705, for Method of PreparingPolyethylene Glycol Modified Polyester Filaments; U.S. Pat. No.6,322,886, for Nonwoven Fabrics Formed from Polyethylene Glycol ModifiedPolyester Fibers and Method for Making the Same; U.S. Pat. No.6,303,739, for Method of Preparing Polyethylene Glycol ModifiedPolyester Filaments; and U.S. Pat. No. 6,291,066, for PolyethyleneGlycol Modified Polyester Fibers and Method for Making the Same.

In the specification and the figures, typical embodiments of theinvention have been disclosed. Specific terms have been used only in ageneric and descriptive sense, and not for purposes of limitation.

1. A polyethylene terephthalate resin, comprising: polyethyleneterephthalate polymers including between about 2 and 6 mole percentcomonomer substitution; between about 2 and 50 ppm of elementaltitanium; less than about 100 ppm of elemental antimony, if any; morethan about 20 ppm of elemental phosphorus; branching agent; and heat-uprate additive that is present in the resin in an amount sufficient toimprove the resin's reheating profile; and nucleating agent, if any, inan amount that is insufficient to significantly decrease heatingcrystallization exotherm peak temperature (T_(CH)); wherein thepolyethylene terephthalate resin has an L* value of more than about 65as classified in the CIE L*a*b* color space.
 2. A polyethyleneterephthalate resin according to claim 1, comprising nucleating agent,if any, in an amount that is insufficient to decrease heatingcrystallization exotherm peak temperature (T_(CH)) below about 140° C.at a heating rate of 10° C. per minute as measured by differentialscanning calorimetry.
 3. A polyethylene terephthalate resin according toclaim 1, comprising less than about 20 ppm of elemental titanium.
 4. Apolyethylene terephthalate resin according to claim 1, furthercomprising between about 15 and 40 ppm of elemental cobalt.
 5. Apolyethylene terephthalate resin according to claim 1, comprisingbranching agent in an amount greater than zero and less than about 0.4percent mole-equivalent branches per mole of standardized polymer, thestandardized polymer being unmodified polyethylene terephthalate.
 6. Apolyethylene terephthalate resin according to claim 1, comprisingbranching agent in an amount between about 0.02 and 0.2 percentmole-equivalent branches per mole of standardized polymer, thestandardized polymer being unmodified polyethylene terephthalate.
 7. Apolyethylene terephthalate resin according to claim 1, comprisingbranching agent in an amount between about 0.04 and 0.075 percentmole-equivalent branches per mole of standardized polymer, thestandardized polymer being unmodified polyethylene terephthalate.
 8. Apolyethylene terephthalate resin according to claim 1, wherein thepolyethylene terephthalate resin has an absorbance (A) of at least about0.18 cm⁻¹ at a wavelength of 1100 nm or at a wavelength of 1280 nm.
 9. Apolyethylene terephthalate resin according to claim 1, wherein thepolyethylene terephthalate resin has an absorbance (A) of at least about0.25 cm⁻¹ at a wavelength of 1100 nm or at a wavelength of 1280 nm. 10.A polyethylene terephthalate resin according to claim 1, wherein thepolyethylene terephthalate resin has an L* value of more than about 75as classified in the CIE L*a*b* color space.
 11. A polyethyleneterephthalate resin according to claim 1, wherein the polyethyleneterephthalate resin has an intrinsic viscosity greater than about 0.68dL/g.
 12. An article according to claim 1, wherein the article comprisesa film, a sheet, a preform, or a container.
 13. A polyethyleneterephthalate resin, comprising: polyethylene terephthalate polymersincluding less than about 6 mole percent comonomer substitution; betweenabout 2 and 25 ppm of elemental titanium; less than about 75 ppm ofelemental antimony, if any; more than about 15 ppm of elementalphosphorus; branching agent that is present in the resin in an amountgreater than 0 and less than 0.1 mole percent; and a heat-up rateadditive that is present in the resin in an amount greater than 0 ppmand less than about 300 ppm; and nucleating agent, if any, in an amountthat is insufficient to decrease heating crystallization exotherm peaktemperature (T_(CH)) below about 140° C. at a heating rate of 10° C. perminute as measured by differential scanning calorimetry; wherein thepolyethylene terephthalate resin has an L* value of more than about 70as classified in the CIE L*a*b* color space.
 14. A polyethyleneterephthalate resin according to claim 13, wherein the polyethyleneterephthalate polymers include between about 2 and 5 mole percentcomonomer substitution.
 15. A polyethylene terephthalate resin accordingto claim 13, comprising: less than about 50 ppm of elemental antimony,if any; and less than about 20 ppm of elemental germanium, if any.
 16. Apolyethylene terephthalate resin according to claim 13, wherein thepolyethylene terephthalate resin has an absorbance (A) of at least about0.20 cm⁻¹ at a wavelength of 1100 nm and at a wavelength of 1280 nm. 17.A polyethylene terephthalate resin, comprising: polyethyleneterephthalate polymers including between about 2 and 6 mole percentcomonomer substitution; between about 2 and 20 ppm of elementaltitanium; less than about 25 ppm of elemental antimony, if any; morethan about 5 ppm of elemental phosphorus; branching agent; and a heat-uprate additive comprising (i) a metal-containing heat-up rate additivethat is present in the resin in an amount between about 10 and 300 ppm,and/or (ii) a carbon-based heat-up rate additive that is present in theresin in an amount greater than 0 ppm and less than about 25 ppm; andnucleating agent, if any, in an amount that is insufficient to decreaseheating crystallization exotherm peak temperature (T_(CH)) below about140° C. at a heating rate of 10° C. per minute as measured bydifferential scanning calorimetry; wherein the polyethyleneterephthalate resin has an L* value of more than about 65 as classifiedin the CIE L*a*b* color space.
 18. A polyethylene terephthalate resinaccording to claim 17, comprising branching agent in an amount betweenabout 0.01 and 0.1 percent mole-equivalent branches per mole ofstandardized polymer, the standardized polymer being unmodifiedpolyethylene terephthalate.
 19. A polyethylene terephthalate resinaccording to claim 17, wherein the polyethylene terephthalate resin hasan L* value of more than about 70 as classified in the CIE L*a*b* colorspace.
 20. A polyethylene terephthalate resin according to claim 17,wherein the polyethylene terephthalate resin possesses a b* color valueof between −3 and 2 as classified by the CIE L*a*b* color space.